TNBGGA: The No Bullshit Guide to Genetic Analysis

The principles of geneplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) regulation were first worked out by Francois Jacob and Jacques Monod in the 1960s-1970s studying the E. coliplugin-autotooltip__default plugin-autotooltip_bigEscherichia coli: an enteric bacterium used both as a model organism and as a utility organism in genetics research. E. coli is commonly used to host various cloning vectors, such as plasmids, cosmids, F factors, and bacterial artificiak chromosomes (BACs). genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) required for cells to use the sugar lactose as a nutrient.

The LacY and LacZ proteinsplugin-autotooltip__default plugin-autotooltip_bigProtein: a molecule that is formed by the translation of messenger RNAs (mRNAs). Functions that proteins provide are what usually give organisms their phenotypes. (formal names for the permease and β-galactosidase enzymesplugin-autotooltip__default plugin-autotooltip_bigEnzyme: a macromolecule, usually a protein (but sometimes an RNA), that functions as a catalyst of some kind of biochemical reaction., respectively) are not expressedplugin-autotooltip__default plugin-autotooltip_bigExpression: a term used to describe the idea that the function of a gene is apparent and can be observed. Genes may not always be expressed all the time in all places. (produced) by the cell until an inducerplugin-autotooltip__default plugin-autotooltip_bigInducer: a molecule that triggers the expression of a gene or genes. Examples in E. coli include lactose and IPTG, which induce expression of the Lac operon in E. coli, and maltose, which induces expression of the Mal operon. An example in yeast is galactose, which induces expression of Gal genes. molecule such as lactose is present in the environment (Fig. 1). Both the $lacY$ and $lacZ$ genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) are part of a cluster of genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) that are regulated together called an operonplugin-autotooltip__default plugin-autotooltip_bigOperon: two or more genes that are transcribed together on an mRNA from a single promoter. Most commonly seen in bacteria; very rare in eukaryotes.. The logic of the Lac operonplugin-autotooltip__default plugin-autotooltip_bigLac operon: an operon in E. coli that contains the cis-acting regulatory elements $lacP$ and $lacO$, and the protein coding genes $lacZ$, $lacY$, and $lacA$. The Lac operon is an example of a negatively-regulated operon. is that the proteinsplugin-autotooltip__default plugin-autotooltip_bigProtein: a molecule that is formed by the translation of messenger RNAs (mRNAs). Functions that proteins provide are what usually give organisms their phenotypes. required by the cell to use lactose as a food source are only made when the lactose is available. This prevents wasteful expressionplugin-autotooltip__default plugin-autotooltip_bigExpression: a term used to describe the idea that the function of a gene is apparent and can be observed. Genes may not always be expressed all the time in all places. of proteinsplugin-autotooltip__default plugin-autotooltip_bigProtein: a molecule that is formed by the translation of messenger RNAs (mRNAs). Functions that proteins provide are what usually give organisms their phenotypes. and enzymesplugin-autotooltip__default plugin-autotooltip_bigEnzyme: a macromolecule, usually a protein (but sometimes an RNA), that functions as a catalyst of some kind of biochemical reaction. when their substratesplugin-autotooltip__default plugin-autotooltip_bigSubstrate: a molecule that undergoes a biochemical reaction catalyzed by an enzyme. By inference, a substrate physically binds to its cognate enzyme. are not available. We say that the Lac genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) are inducibleplugin-autotooltip__default plugin-autotooltip_bigInducible: a term describing a pattern of gene expression, wherein genes or operons are not expressed until some kind of condition is met, e.g., inducer is present. Not all genes are naturally inducible; some genes are naturally constitutive..

At first, scientists noted that lactose is both an inducerplugin-autotooltip__default plugin-autotooltip_bigInducer: a molecule that triggers the expression of a gene or genes. Examples in E. coli include lactose and IPTG, which induce expression of the Lac operon in E. coli, and maltose, which induces expression of the Mal operon. An example in yeast is galactose, which induces expression of Gal genes. and substrateplugin-autotooltip__default plugin-autotooltip_bigSubstrate: a molecule that undergoes a biochemical reaction catalyzed by an enzyme. By inference, a substrate physically binds to its cognate enzyme. for the enzymesplugin-autotooltip__default plugin-autotooltip_bigEnzyme: a macromolecule, usually a protein (but sometimes an RNA), that functions as a catalyst of some kind of biochemical reaction. of the Lac operonplugin-autotooltip__default plugin-autotooltip_bigLac operon: an operon in E. coli that contains the cis-acting regulatory elements $lacP$ and $lacO$, and the protein coding genes $lacZ$, $lacY$, and $lacA$. The Lac operon is an example of a negatively-regulated operon., and they incorrectly concluded that lactose was somehow acting as a template for the formation of the enzymeplugin-autotooltip__default plugin-autotooltip_bigEnzyme: a macromolecule, usually a protein (but sometimes an RNA), that functions as a catalyst of some kind of biochemical reaction., which obviously makes no sense now, given our current knowledge. Later, compounds were discovered that could act as inducersplugin-autotooltip__default plugin-autotooltip_bigInducer: a molecule that triggers the expression of a gene or genes. Examples in E. coli include lactose and IPTG, which induce expression of the Lac operon in E. coli, and maltose, which induces expression of the Mal operon. An example in yeast is galactose, which induces expression of Gal genes. but were not themselves substratesplugin-autotooltip__default plugin-autotooltip_bigSubstrate: a molecule that undergoes a biochemical reaction catalyzed by an enzyme. By inference, a substrate physically binds to its cognate enzyme. for the Lac enzymesplugin-autotooltip__default plugin-autotooltip_bigEnzyme: a macromolecule, usually a protein (but sometimes an RNA), that functions as a catalyst of some kind of biochemical reaction.. The classic example of such a “gratuitous inducerplugin-autotooltip__default plugin-autotooltip_bigInducer: a molecule that triggers the expression of a gene or genes. Examples in E. coli include lactose and IPTG, which induce expression of the Lac operon in E. coli, and maltose, which induces expression of the Mal operon. An example in yeast is galactose, which induces expression of Gal genes.” is IPTGplugin-autotooltip__default plugin-autotooltip_bigIPTG: isopropyl β-D-1-thiogalactopyranoside, an inducer of the Lac operon. IPTG binds to the Lac repressor protein (also known as LacI). (isopropyl β-D-1-thiogalactopyranoside; Fig. 2), which is an effective inducerplugin-autotooltip__default plugin-autotooltip_bigInducer: a molecule that triggers the expression of a gene or genes. Examples in E. coli include lactose and IPTG, which induce expression of the Lac operon in E. coli, and maltose, which induces expression of the Mal operon. An example in yeast is galactose, which induces expression of Gal genes. of LacZ expressionplugin-autotooltip__default plugin-autotooltip_bigExpression: a term used to describe the idea that the function of a gene is apparent and can be observed. Genes may not always be expressed all the time in all places. but isn’t hydrolyzed by β-galactosidase. The existence of compounds such as IPTGplugin-autotooltip__default plugin-autotooltip_bigIPTG: isopropyl β-D-1-thiogalactopyranoside, an inducer of the Lac operon. IPTG binds to the Lac repressor protein (also known as LacI). shows that recognition of the inducerplugin-autotooltip__default plugin-autotooltip_bigInducer: a molecule that triggers the expression of a gene or genes. Examples in E. coli include lactose and IPTG, which induce expression of the Lac operon in E. coli, and maltose, which induces expression of the Mal operon. An example in yeast is galactose, which induces expression of Gal genes. is a separate molecular event from lactose breakdown.

The next major finding was the discovery of $lacI^–$ mutantsplugin-autotooltip__default plugin-autotooltip_bigMutant: an individual that has a different phenotype than wildtype and likely contains one more mutations that cause this difference.. $lacI^–$ mutantsplugin-autotooltip__default plugin-autotooltip_bigMutant: an individual that has a different phenotype than wildtype and likely contains one more mutations that cause this difference. are constitutiveplugin-autotooltip__default plugin-autotooltip_bigConstitutive: a term describing a pattern of gene expression, wherein the gene is always expressed no matter what. For some genes, constitutive expression is normal (see housekeeping gene). For inducible genes or operons, constitutive is a mutant state., meaning that they always express β-galactosidase at high levels regardless of whether there is an inducerplugin-autotooltip__default plugin-autotooltip_bigInducer: a molecule that triggers the expression of a gene or genes. Examples in E. coli include lactose and IPTG, which induce expression of the Lac operon in E. coli, and maltose, which induces expression of the Mal operon. An example in yeast is galactose, which induces expression of Gal genes. present or not. $lacI^–$ mutantsplugin-autotooltip__default plugin-autotooltip_bigMutant: an individual that has a different phenotype than wildtype and likely contains one more mutations that cause this difference. have apparently lost a component of the machinery the cell uses to turn off β-galactosidase expressionplugin-autotooltip__default plugin-autotooltip_bigExpression: a term used to describe the idea that the function of a gene is apparent and can be observed. Genes may not always be expressed all the time in all places..

We now tell you the story of the Lac operonplugin-autotooltip__default plugin-autotooltip_bigLac operon: an operon in E. coli that contains the cis-acting regulatory elements $lacP$ and $lacO$, and the protein coding genes $lacZ$, $lacY$, and $lacA$. The Lac operon is an example of a negatively-regulated operon. backwards. We first tell you the conclusions that Jacob and Monod made from their experiments. The regulatory system turns out to be quite simple (Fig. 3). Our goal is then to understand how the genetic experiments described below helped them reach those conclusions. The results are interesting and of general importance, but we are more interested in understanding their thinking and how they applied genetics to studying geneplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) expressionplugin-autotooltip__default plugin-autotooltip_bigExpression: a term used to describe the idea that the function of a gene is apparent and can be observed. Genes may not always be expressed all the time in all places..

The general model of the Lac operonplugin-autotooltip__default plugin-autotooltip_bigLac operon: an operon in E. coli that contains the cis-acting regulatory elements $lacP$ and $lacO$, and the protein coding genes $lacZ$, $lacY$, and $lacA$. The Lac operon is an example of a negatively-regulated operon. is that the inducerplugin-autotooltip__default plugin-autotooltip_bigInducer: a molecule that triggers the expression of a gene or genes. Examples in E. coli include lactose and IPTG, which induce expression of the Lac operon in E. coli, and maltose, which induces expression of the Mal operon. An example in yeast is galactose, which induces expression of Gal genes. (which can be either lactose or IPTGplugin-autotooltip__default plugin-autotooltip_bigIPTG: isopropyl β-D-1-thiogalactopyranoside, an inducer of the Lac operon. IPTG binds to the Lac repressor protein (also known as LacI).) has a net positive effect on Lac operonplugin-autotooltip__default plugin-autotooltip_bigLac operon: an operon in E. coli that contains the cis-acting regulatory elements $lacP$ and $lacO$, and the protein coding genes $lacZ$, $lacY$, and $lacA$. The Lac operon is an example of a negatively-regulated operon. expressionplugin-autotooltip__default plugin-autotooltip_bigExpression: a term used to describe the idea that the function of a gene is apparent and can be observed. Genes may not always be expressed all the time in all places. because the inducerplugin-autotooltip__default plugin-autotooltip_bigInducer: a molecule that triggers the expression of a gene or genes. Examples in E. coli include lactose and IPTG, which induce expression of the Lac operon in E. coli, and maltose, which induces expression of the Mal operon. An example in yeast is galactose, which induces expression of Gal genes. is a negative regulatorplugin-autotooltip__default plugin-autotooltip_bigNegative regulator: in the context of gene regulation, a negative regulator is a gene whose activity blocks the expression of another gene. Compare to repressor. of the repressorplugin-autotooltip__default plugin-autotooltip_bigRepressor: a DNA binding protein that binds to negatively acting cis-acting elements such as operators in bacteria to inhibit transcription. Compare to negative regulator. LacIplugin-autotooltip__default plugin-autotooltip_bigLacI: the protein encoded by the $lacI$ gene; also called the Lac repressor protein. Binds to lactose or IPTG; upon binding, it loses the ability to bind to $lacO$., which is itself a negative regulatorplugin-autotooltip__default plugin-autotooltip_bigNegative regulator: in the context of gene regulation, a negative regulator is a gene whose activity blocks the expression of another gene. Compare to repressor. of the geneplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) for β-galactosidase. Some key details are described here:

• The $lacI$ geneplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) codes for the Lac repressor proteinplugin-autotooltip__default plugin-autotooltip_bigLacI: the protein encoded by the $lacI$ gene; also called the Lac repressor protein. Binds to lactose or IPTG; upon binding, it loses the ability to bind to $lacO$., a DNAplugin-autotooltip__default plugin-autotooltip_bigDNA: deoxyribonucleic acid. The genetic material for nearly all life on Earth. binding proteinplugin-autotooltip__default plugin-autotooltip_bigProtein: a molecule that is formed by the translation of messenger RNAs (mRNAs). Functions that proteins provide are what usually give organisms their phenotypes. that binds to a DNAplugin-autotooltip__default plugin-autotooltip_bigDNA: deoxyribonucleic acid. The genetic material for nearly all life on Earth. sequenceplugin-autotooltip__default plugin-autotooltip_bigSequence: the precise order of monomers in a polymer. In DNA, it refers to the order of G, A, T, and C nucleotides. In RNA, it refers to the order of G, A, U, and C nucleotides. In proteins, it refers to the order of amino acids. called $lacO$. Lac repressor proteinplugin-autotooltip__default plugin-autotooltip_bigLacI: the protein encoded by the $lacI$ gene; also called the Lac repressor protein. Binds to lactose or IPTG; upon binding, it loses the ability to bind to $lacO$. is always made, regardless of whether there is inducerplugin-autotooltip__default plugin-autotooltip_bigInducer: a molecule that triggers the expression of a gene or genes. Examples in E. coli include lactose and IPTG, which induce expression of the Lac operon in E. coli, and maltose, which induces expression of the Mal operon. An example in yeast is galactose, which induces expression of Gal genes. present.
• RNA polymeraseplugin-autotooltip__default plugin-autotooltip_bigRNA polymerase: the enzyme that carries out RNA transcription. There are many different types of RNA polymerase, but in this book we collectively refer to them as just “RNA polymerase” for simplicity. binds to a DNAplugin-autotooltip__default plugin-autotooltip_bigDNA: deoxyribonucleic acid. The genetic material for nearly all life on Earth. sequenceplugin-autotooltip__default plugin-autotooltip_bigSequence: the precise order of monomers in a polymer. In DNA, it refers to the order of G, A, T, and C nucleotides. In RNA, it refers to the order of G, A, U, and C nucleotides. In proteins, it refers to the order of amino acids. called $lacP$, also called the promoterplugin-autotooltip__default plugin-autotooltip_bigPromoter: has multiple closely related but subtly different meanings depending on context:
  
  * In bacteria, a promoter is a cis-acting DNA sequence near the transcription start site of a gene or operon that binds to bacterial RNA polymerase. * In eukaryotes, the formal definition of a promoter (also called a basal promoter) is a RNA. RNA polymeraseplugin-autotooltip__default plugin-autotooltip_bigRNA polymerase: the enzyme that carries out RNA transcription. There are many different types of RNA polymerase, but in this book we collectively refer to them as just “RNA polymerase” for simplicity. binds to $lacP$, also regardless of whether there is inducerplugin-autotooltip__default plugin-autotooltip_bigInducer: a molecule that triggers the expression of a gene or genes. Examples in E. coli include lactose and IPTG, which induce expression of the Lac operon in E. coli, and maltose, which induces expression of the Mal operon. An example in yeast is galactose, which induces expression of Gal genes. present.
• Lac repressor proteinplugin-autotooltip__default plugin-autotooltip_bigLacI: the protein encoded by the $lacI$ gene; also called the Lac repressor protein. Binds to lactose or IPTG; upon binding, it loses the ability to bind to $lacO$. normally prevents RNA polymeraseplugin-autotooltip__default plugin-autotooltip_bigRNA polymerase: the enzyme that carries out RNA transcription. There are many different types of RNA polymerase, but in this book we collectively refer to them as just “RNA polymerase” for simplicity. from transcribing the mRNAplugin-autotooltip__default plugin-autotooltip_bigmessenger RNA (mRNA): an RNA molecule that codes for protein. for the $lacZ$, $lacY$, and $lacA$ genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-). It acts like a roadblock for RNA polymeraseplugin-autotooltip__default plugin-autotooltip_bigRNA polymerase: the enzyme that carries out RNA transcription. There are many different types of RNA polymerase, but in this book we collectively refer to them as just “RNA polymerase” for simplicity..
• When inducerplugin-autotooltip__default plugin-autotooltip_bigInducer: a molecule that triggers the expression of a gene or genes. Examples in E. coli include lactose and IPTG, which induce expression of the Lac operon in E. coli, and maltose, which induces expression of the Mal operon. An example in yeast is galactose, which induces expression of Gal genes. (either lactose or IPTGplugin-autotooltip__default plugin-autotooltip_bigIPTG: isopropyl β-D-1-thiogalactopyranoside, an inducer of the Lac operon. IPTG binds to the Lac repressor protein (also known as LacI).) is present, it binds to Lac repressor proteinplugin-autotooltip__default plugin-autotooltip_bigLacI: the protein encoded by the $lacI$ gene; also called the Lac repressor protein. Binds to lactose or IPTG; upon binding, it loses the ability to bind to $lacO$. and causes it to detach from the $lacO$ DNAplugin-autotooltip__default plugin-autotooltip_bigDNA: deoxyribonucleic acid. The genetic material for nearly all life on Earth.. With the roadblock removed, RNA polymeraseplugin-autotooltip__default plugin-autotooltip_bigRNA polymerase: the enzyme that carries out RNA transcription. There are many different types of RNA polymerase, but in this book we collectively refer to them as just “RNA polymerase” for simplicity. is then able to transcribeplugin-autotooltip__default plugin-autotooltip_bigRNA transcription: the process of RNA polymerase using the DNA sequence of a gene as a template to form an mRNA (in prokaryotes) or pre-mRNA (in eukaryotes). In most cases, “transcription” implies RNA transcription. the mRNAplugin-autotooltip__default plugin-autotooltip_bigmessenger RNA (mRNA): an RNA molecule that codes for protein. for the Lac genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-).

We will now consider how regulatory mutantsplugin-autotooltip__default plugin-autotooltip_bigMutant: an individual that has a different phenotype than wildtype and likely contains one more mutations that cause this difference. can be analyzed genetically. In essence, we want to know how Jacob and Monod figured out the mechanism described above. We will use as examples different mutationsplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant. in the Lac system, but these genetic tests are very general and can be applied to most regulatory systems. For instance, in Chap. 13 we will see how these concepts (but not the technical details) can be applied to studying geneplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) regulation in yeastplugin-autotooltip__default plugin-autotooltip_bigYeast: in this book, refers to Saccharomyces cerevisiae, a single-celled eukaryotic microbe used as a model genetic organism. See Chapter 02. The concepts are more important than the technical details!

Using the dominanceplugin-autotooltip__default plugin-autotooltip_bigDominant: used to describe an allele, usually in comparison to wildtype. Dominant alleles will express their phenotype when combined with a wildtype allele. test in separate experiments, Jacob and Monod established that the $lacI^-$ and $lacZ^-$ mutationsplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant. are recessiveplugin-autotooltip__default plugin-autotooltip_bigRecessive: used to describe an allele, usually in comparison to wildtype. Recessive alleles do not exhibit their phenotype when combined with a wildtype allele., which suggested that they are probably loss of functionplugin-autotooltip__default plugin-autotooltip_bigLoss of function: a general term used to describe mutant alleles that have less activity than wildtype. Amorphic and hypomorphic mutations are loss of function mutations. mutationsplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant. (Table 1). Also, since they are recessiveplugin-autotooltip__default plugin-autotooltip_bigRecessive: used to describe an allele, usually in comparison to wildtype. Recessive alleles do not exhibit their phenotype when combined with a wildtype allele., this further allows us to use the complementation testplugin-autotooltip__default plugin-autotooltip_bigComplementation test: a genetic experiment that answers the question: how many different genes are represented within a collection of mutants? to determine whether the mutationsplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant. are in two different genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-). It turns out that they are indeed different genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-), because $lacI$ and $lacZ$ complementplugin-autotooltip__default plugin-autotooltip_bigComplement: used to describe the relationship between two recessive mutants. If a diploid created by mating the two mutants has a wildtype phenotype, we say the two mutants complement each other. each other. Jacob and Monod reasoned that since $lacI$ mutationsplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant. cause a lactose-metabolizing enzymeplugin-autotooltip__default plugin-autotooltip_bigEnzyme: a macromolecule, usually a protein (but sometimes an RNA), that functions as a catalyst of some kind of biochemical reaction. (β -galactosidase) to always be produced, $lacI$ itself probably doesn't code for a lactose-metabolizing enzymeplugin-autotooltip__default plugin-autotooltip_bigEnzyme: a macromolecule, usually a protein (but sometimes an RNA), that functions as a catalyst of some kind of biochemical reaction.. Rather, its gene productplugin-autotooltip__default plugin-autotooltip_bigGene product: the molecule that is produced based on information contained within a gene and provides function to the organism. Most of the time, a gene product is a protein. Sometimes gene products can also be an RNA molecule. In forward genetic analysis, we can't formally tell if a gene product is probably regulates the function or production of β-galactosidase by “shutting it down”. Conversely, since $lacZ$ mutantsplugin-autotooltip__default plugin-autotooltip_bigMutant: an individual that has a different phenotype than wildtype and likely contains one more mutations that cause this difference. cannot produce β-galactosidase no matter what, $lacZ$ either positively regulates the production of β-galactosidase or codes for β-galactosidase itself (it winds up that the latter is true).

A second type of constitutiveplugin-autotooltip__default plugin-autotooltip_bigConstitutive: a term describing a pattern of gene expression, wherein the gene is always expressed no matter what. For some genes, constitutive expression is normal (see housekeeping gene). For inducible genes or operons, constitutive is a mutant state. mutantplugin-autotooltip__default plugin-autotooltip_bigMutant: an individual that has a different phenotype than wildtype and likely contains one more mutations that cause this difference. is known as a $lacO^c$ mutationplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant.. We later learn that this type of mutationplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant. inactivates the $lacO$ operatorplugin-autotooltip__default plugin-autotooltip_bigOperator: in bacterial genetics, an operator is a cis-acting genetic element that negatively regulates the expression of nearby genes. $lacO$ of the Lac operon is an example of an operator. site. $lacO^c$ mutationsplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant. are dominantplugin-autotooltip__default plugin-autotooltip_bigDominant: used to describe an allele, usually in comparison to wildtype. Dominant alleles will express their phenotype when combined with a wildtype allele. as revealed in tests of the appropriate merodiploidsplugin-autotooltip__default plugin-autotooltip_bigMerodiploid: used to describe an organism that is naturally haploid but is partially diploid for a portion of its genome due to the presence of an episome that contains a chromosomal fragment.:

Based on other information, Jacob and Monod actually knew that $lacI$ and $lacO$ are different genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) because they mapped to completely different locations on the E. coliplugin-autotooltip__default plugin-autotooltip_bigEscherichia coli: an enteric bacterium used both as a model organism and as a utility organism in genetics research. E. coli is commonly used to host various cloning vectors, such as plasmids, cosmids, F factors, and bacterial artificiak chromosomes (BACs). chromosomeplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins. (i.e., they are different genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) based on a test of position; Chap. 05). In fact, $lacO$ mapped very close to $lacZ$, whereas $lacI$ is farther away from $lacZ$. However, if you didn't know their map positions, at a first glance the only difference between $lacO^c$ and $lacI^-$ is that $lacO^c$ is dominantplugin-autotooltip__default plugin-autotooltip_bigDominant: used to describe an allele, usually in comparison to wildtype. Dominant alleles will express their phenotype when combined with a wildtype allele. and $lacI^-$ is recessiveplugin-autotooltip__default plugin-autotooltip_bigRecessive: used to describe an allele, usually in comparison to wildtype. Recessive alleles do not exhibit their phenotype when combined with a wildtype allele.; therefore, you might think that on the basis of a dominanceplugin-autotooltip__default plugin-autotooltip_bigDominant: used to describe an allele, usually in comparison to wildtype. Dominant alleles will express their phenotype when combined with a wildtype allele. test we could tell whether we have a $lacO^c$ or a $lacI^–$ mutationplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant.. However, life is not so simple, because it is possible to find $lacI^–$ mutationsplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant. that are dominantplugin-autotooltip__default plugin-autotooltip_bigDominant: used to describe an allele, usually in comparison to wildtype. Dominant alleles will express their phenotype when combined with a wildtype allele.. Such mutationsplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant. are known as $lacI^{-d}$. “$-d$” stands for dominant negativeplugin-autotooltip__default plugin-autotooltip_bigAntimorphic mutation: A mutation that, when combined with a wildtype allele (either as a merodiploid or as a diploid), the total amount of activity is less than wildtype. The implication is that the gene product produced by the antimorphic allele interferes with the function of the wildtype gene product. Also called a dominant negative allele.; dominant negativeplugin-autotooltip__default plugin-autotooltip_bigAntimorphic mutation: A mutation that, when combined with a wildtype allele (either as a merodiploid or as a diploid), the total amount of activity is less than wildtype. The implication is that the gene product produced by the antimorphic allele interferes with the function of the wildtype gene product. Also called a dominant negative allele. mutationsplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant. are similar to recessiveplugin-autotooltip__default plugin-autotooltip_bigRecessive: used to describe an allele, usually in comparison to wildtype. Recessive alleles do not exhibit their phenotype when combined with a wildtype allele. loss of functionplugin-autotooltip__default plugin-autotooltip_bigLoss of function: a general term used to describe mutant alleles that have less activity than wildtype. Amorphic and hypomorphic mutations are loss of function mutations. mutationsplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant. in that they both have similar loss of functionplugin-autotooltip__default plugin-autotooltip_bigLoss of function: a general term used to describe mutant alleles that have less activity than wildtype. Amorphic and hypomorphic mutations are loss of function mutations. phenotypesplugin-autotooltip__default plugin-autotooltip_bigPhenotype: an observable feature or property of an organism., except one is dominantplugin-autotooltip__default plugin-autotooltip_bigDominant: used to describe an allele, usually in comparison to wildtype. Dominant alleles will express their phenotype when combined with a wildtype allele. and one is recessiveplugin-autotooltip__default plugin-autotooltip_bigRecessive: used to describe an allele, usually in comparison to wildtype. Recessive alleles do not exhibit their phenotype when combined with a wildtype allele.. Another name for dominant negativeplugin-autotooltip__default plugin-autotooltip_bigAntimorphic mutation: A mutation that, when combined with a wildtype allele (either as a merodiploid or as a diploid), the total amount of activity is less than wildtype. The implication is that the gene product produced by the antimorphic allele interferes with the function of the wildtype gene product. Also called a dominant negative allele. is antimorphicplugin-autotooltip__default plugin-autotooltip_bigAntimorphic mutation: A mutation that, when combined with a wildtype allele (either as a merodiploid or as a diploid), the total amount of activity is less than wildtype. The implication is that the gene product produced by the antimorphic allele interferes with the function of the wildtype gene product. Also called a dominant negative allele. (see Chap. 8).

$lacO^c$ and $lacI^{-d}$ are both dominantplugin-autotooltip__default plugin-autotooltip_bigDominant: used to describe an allele, usually in comparison to wildtype. Dominant alleles will express their phenotype when combined with a wildtype allele., so we can't use the complementation testplugin-autotooltip__default plugin-autotooltip_bigComplementation test: a genetic experiment that answers the question: how many different genes are represented within a collection of mutants? to determine if they are allelic to each other. We need a different test to help us distinguish between $lacO^c$ and $lacI^{-d}$. We will now consider a new genetic test that will let us distinguish $lacO^c$ operatorplugin-autotooltip__default plugin-autotooltip_bigOperator: in bacterial genetics, an operator is a cis-acting genetic element that negatively regulates the expression of nearby genes. $lacO$ of the Lac operon is an example of an operator. constitutiveplugin-autotooltip__default plugin-autotooltip_bigConstitutive: a term describing a pattern of gene expression, wherein the gene is always expressed no matter what. For some genes, constitutive expression is normal (see housekeeping gene). For inducible genes or operons, constitutive is a mutant state. from $lacI^{-d}$ repressorplugin-autotooltip__default plugin-autotooltip_bigRepressor: a DNA binding protein that binds to negatively acting cis-acting elements such as operators in bacteria to inhibit transcription. Compare to negative regulator. dominant negativeplugin-autotooltip__default plugin-autotooltip_bigAntimorphic mutation: A mutation that, when combined with a wildtype allele (either as a merodiploid or as a diploid), the total amount of activity is less than wildtype. The implication is that the gene product produced by the antimorphic allele interferes with the function of the wildtype gene product. Also called a dominant negative allele. mutationsplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant.. This test is informative because it gives us further clues in understanding how the various Lac genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) function.

Jacob and Monod found that the physical location of genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) relative to each other affected their function. Unlike eukaryotesplugin-autotooltip__default plugin-autotooltip_bigeukaryote: organism whose cells have membrane bound organelles, including the nucleus., E. coliplugin-autotooltip__default plugin-autotooltip_bigEscherichia coli: an enteric bacterium used both as a model organism and as a utility organism in genetics research. E. coli is commonly used to host various cloning vectors, such as plasmids, cosmids, F factors, and bacterial artificiak chromosomes (BACs). only has a single chromosomeplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins.. Therefore, all genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) on the chromosomeplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins. are on the same DNAplugin-autotooltip__default plugin-autotooltip_bigDNA: deoxyribonucleic acid. The genetic material for nearly all life on Earth. molecule. Note in Table 4 that $lacI^{-d}$ is dominantplugin-autotooltip__default plugin-autotooltip_bigDominant: used to describe an allele, usually in comparison to wildtype. Dominant alleles will express their phenotype when combined with a wildtype allele. no matter whether it is on the same piece of DNAplugin-autotooltip__default plugin-autotooltip_bigDNA: deoxyribonucleic acid. The genetic material for nearly all life on Earth. as $lacZ^+$ (on the E. coliplugin-autotooltip__default plugin-autotooltip_bigEscherichia coli: an enteric bacterium used both as a model organism and as a utility organism in genetics research. E. coli is commonly used to host various cloning vectors, such as plasmids, cosmids, F factors, and bacterial artificiak chromosomes (BACs). chromosomeplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins.; another way to say this is “in cisplugin-autotooltip__default plugin-autotooltip_bigCis and trans: In genetics, cis and trans are terms used to describe the relative physical locations of genes or genetic elements. If two genes are in cis, this means that they are physically located on the same DNA molecule. If two genes are in trans, this means that they are physically located on two different”) or a different piece of DNAplugin-autotooltip__default plugin-autotooltip_bigDNA: deoxyribonucleic acid. The genetic material for nearly all life on Earth. as $lacZ^+$ (on the $F'$ plasmidplugin-autotooltip__default plugin-autotooltip_bigPlasmid: a circular episome found in bacteria and yeast. Plasmids are commonly used as cloning vectors.; another way to say this is “in transplugin-autotooltip__default plugin-autotooltip_bigCis and trans: In genetics, cis and trans are terms used to describe the relative physical locations of genes or genetic elements. If two genes are in cis, this means that they are physically located on the same DNA molecule. If two genes are in trans, this means that they are physically located on two different”). By contrast, $lacO^c$ is only dominantplugin-autotooltip__default plugin-autotooltip_bigDominant: used to describe an allele, usually in comparison to wildtype. Dominant alleles will express their phenotype when combined with a wildtype allele. if it acts in cisplugin-autotooltip__default plugin-autotooltip_bigCis and trans: In genetics, cis and trans are terms used to describe the relative physical locations of genes or genetic elements. If two genes are in cis, this means that they are physically located on the same DNA molecule. If two genes are in trans, this means that they are physically located on two different; that is, $lacO^c$ only exhibits its dominantplugin-autotooltip__default plugin-autotooltip_bigDominant: used to describe an allele, usually in comparison to wildtype. Dominant alleles will express their phenotype when combined with a wildtype allele. effect when it is on the same piece of DNAplugin-autotooltip__default plugin-autotooltip_bigDNA: deoxyribonucleic acid. The genetic material for nearly all life on Earth. as $lacZ^+$. Jacob and Monod explained this by theorizing that the $lacI$ geneplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) must produce a proteinplugin-autotooltip__default plugin-autotooltip_bigProtein: a molecule that is formed by the translation of messenger RNAs (mRNAs). Functions that proteins provide are what usually give organisms their phenotypes. that is able to diffuse and attach to either chromosomalplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins. DNAplugin-autotooltip__default plugin-autotooltip_bigDNA: deoxyribonucleic acid. The genetic material for nearly all life on Earth. or $F'$ plasmidplugin-autotooltip__default plugin-autotooltip_bigPlasmid: a circular episome found in bacteria and yeast. Plasmids are commonly used as cloning vectors. DNAplugin-autotooltip__default plugin-autotooltip_bigDNA: deoxyribonucleic acid. The genetic material for nearly all life on Earth.. They further hypothesized that $lacO$ (which they also knew was very closely linkedplugin-autotooltip__default plugin-autotooltip_bigLinkage: two loci are linked to each other if they are less than 50 m.u. apart. Two loci are unlinked if they are either (1) greater than 50 m.u. apart on the same chromosome, or; (2) are on separate chromosomes. to $lacZ$) represented not a proteinplugin-autotooltip__default plugin-autotooltip_bigProtein: a molecule that is formed by the translation of messenger RNAs (mRNAs). Functions that proteins provide are what usually give organisms their phenotypes.-producing geneplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) but rather a DNAplugin-autotooltip__default plugin-autotooltip_bigDNA: deoxyribonucleic acid. The genetic material for nearly all life on Earth. sequenceplugin-autotooltip__default plugin-autotooltip_bigSequence: the precise order of monomers in a polymer. In DNA, it refers to the order of G, A, T, and C nucleotides. In RNA, it refers to the order of G, A, U, and C nucleotides. In proteins, it refers to the order of amino acids. that controlled $lacZ$ expressionplugin-autotooltip__default plugin-autotooltip_bigExpression: a term used to describe the idea that the function of a gene is apparent and can be observed. Genes may not always be expressed all the time in all places. - and it only worked if $lacO$ was physically linkedplugin-autotooltip__default plugin-autotooltip_bigLinkage: two loci are linked to each other if they are less than 50 m.u. apart. Two loci are unlinked if they are either (1) greater than 50 m.u. apart on the same chromosome, or; (2) are on separate chromosomes. to $lacZ$ on the same piece of DNAplugin-autotooltip__default plugin-autotooltip_bigDNA: deoxyribonucleic acid. The genetic material for nearly all life on Earth..

The concept of cisplugin-autotooltip__default plugin-autotooltip_bigCis and trans: In genetics, cis and trans are terms used to describe the relative physical locations of genes or genetic elements. If two genes are in cis, this means that they are physically located on the same DNA molecule. If two genes are in trans, this means that they are physically located on two different- and transplugin-autotooltip__default plugin-autotooltip_bigCis and trans: In genetics, cis and trans are terms used to describe the relative physical locations of genes or genetic elements. If two genes are in cis, this means that they are physically located on the same DNA molecule. If two genes are in trans, this means that they are physically located on two different-acting factors applies to eukaryoticplugin-autotooltip__default plugin-autotooltip_bigeukaryote: organism whose cells have membrane bound organelles, including the nucleus. geneplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) regulation as well. In fact, proteinsplugin-autotooltip__default plugin-autotooltip_bigProtein: a molecule that is formed by the translation of messenger RNAs (mRNAs). Functions that proteins provide are what usually give organisms their phenotypes. that bind to DNAplugin-autotooltip__default plugin-autotooltip_bigDNA: deoxyribonucleic acid. The genetic material for nearly all life on Earth. and activate geneplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) transcriptionplugin-autotooltip__default plugin-autotooltip_bigRNA transcription: the process of RNA polymerase using the DNA sequence of a gene as a template to form an mRNA (in prokaryotes) or pre-mRNA (in eukaryotes). In most cases, “transcription” implies RNA transcription. (even in eukaryotesplugin-autotooltip__default plugin-autotooltip_bigeukaryote: organism whose cells have membrane bound organelles, including the nucleus.) are sometimes called transactivatorsplugin-autotooltip__default plugin-autotooltip_bigTransactivator (activator): a DNA binding protein that binds to promoter sequences to activate the transcription of nearby genes. In the context of gene expression, “activator” is usually a synonym for transactivator. Compare with positive regulator.. So far, we've seen that the Lac operonplugin-autotooltip__default plugin-autotooltip_bigLac operon: an operon in E. coli that contains the cis-acting regulatory elements $lacP$ and $lacO$, and the protein coding genes $lacZ$, $lacY$, and $lacA$. The Lac operon is an example of a negatively-regulated operon. is negatively regulated; that is, the default state of the Lac operonplugin-autotooltip__default plugin-autotooltip_bigLac operon: an operon in E. coli that contains the cis-acting regulatory elements $lacP$ and $lacO$, and the protein coding genes $lacZ$, $lacY$, and $lacA$. The Lac operon is an example of a negatively-regulated operon. is that it is expressedplugin-autotooltip__default plugin-autotooltip_bigExpression: a term used to describe the idea that the function of a gene is apparent and can be observed. Genes may not always be expressed all the time in all places., but the $lacO$ repressorplugin-autotooltip__default plugin-autotooltip_bigRepressor: a DNA binding protein that binds to negatively acting cis-acting elements such as operators in bacteria to inhibit transcription. Compare to negative regulator. inactivates expressionplugin-autotooltip__default plugin-autotooltip_bigExpression: a term used to describe the idea that the function of a gene is apparent and can be observed. Genes may not always be expressed all the time in all places. unless an inducerplugin-autotooltip__default plugin-autotooltip_bigInducer: a molecule that triggers the expression of a gene or genes. Examples in E. coli include lactose and IPTG, which induce expression of the Lac operon in E. coli, and maltose, which induces expression of the Mal operon. An example in yeast is galactose, which induces expression of Gal genes. is present. In the next section, we will see an example of a transactivatorplugin-autotooltip__default plugin-autotooltip_bigTransactivator (activator): a DNA binding protein that binds to promoter sequences to activate the transcription of nearby genes. In the context of gene expression, “activator” is usually a synonym for transactivator. Compare with positive regulator. in E. coliplugin-autotooltip__default plugin-autotooltip_bigEscherichia coli: an enteric bacterium used both as a model organism and as a utility organism in genetics research. E. coli is commonly used to host various cloning vectors, such as plasmids, cosmids, F factors, and bacterial artificiak chromosomes (BACs). called MalTplugin-autotooltip__default plugin-autotooltip_bigMalT: a protein encoded by the $malT$ gene that acts as a transactivator for the Mal operon..

To understand positive regulation, we first need a little more background information on uninducibleplugin-autotooltip__default plugin-autotooltip_bigUninducible: a mutant state wherein normally inducible genes are no longer inducible (and in fact may no longer be expressed at all). mutationsplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant. in the Lac operonplugin-autotooltip__default plugin-autotooltip_bigLac operon: an operon in E. coli that contains the cis-acting regulatory elements $lacP$ and $lacO$, and the protein coding genes $lacZ$, $lacY$, and $lacA$. The Lac operon is an example of a negatively-regulated operon.. Until now we have been mostly considering mutationsplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant. that lead to constitutiveplugin-autotooltip__default plugin-autotooltip_bigConstitutive: a term describing a pattern of gene expression, wherein the gene is always expressed no matter what. For some genes, constitutive expression is normal (see housekeeping gene). For inducible genes or operons, constitutive is a mutant state. synthesis of β-galactosidase. It is also possible to get mutationsplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant. that are uninducibleplugin-autotooltip__default plugin-autotooltip_bigUninducible: a mutant state wherein normally inducible genes are no longer inducible (and in fact may no longer be expressed at all).¹⁾. For example, a mutationplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant. in the promoterplugin-autotooltip__default plugin-autotooltip_bigPromoter: has multiple closely related but subtly different meanings depending on context:

* In bacteria, a promoter is a cis-acting DNA sequence near the transcription start site of a gene or operon that binds to bacterial RNA polymerase. * In eukaryotes, the formal definition of a promoter (also called a basal promoter) is a RNA ($lacP^-$) is uninducibleplugin-autotooltip__default plugin-autotooltip_bigUninducible: a mutant state wherein normally inducible genes are no longer inducible (and in fact may no longer be expressed at all). (Table Tab5). $lacP^-$ promoterplugin-autotooltip__default plugin-autotooltip_bigPromoter: has multiple closely related but subtly different meanings depending on context:

* In bacteria, a promoter is a cis-acting DNA sequence near the transcription start site of a gene or operon that binds to bacterial RNA polymerase. * In eukaryotes, the formal definition of a promoter (also called a basal promoter) is a RNA mutantsplugin-autotooltip__default plugin-autotooltip_bigMutant: an individual that has a different phenotype than wildtype and likely contains one more mutations that cause this difference. in the Lac operonplugin-autotooltip__default plugin-autotooltip_bigLac operon: an operon in E. coli that contains the cis-acting regulatory elements $lacP$ and $lacO$, and the protein coding genes $lacZ$, $lacY$, and $lacA$. The Lac operon is an example of a negatively-regulated operon. can be distinguished from simple $lacZ^–$ mutationsplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant. since promoterplugin-autotooltip__default plugin-autotooltip_bigPromoter: has multiple closely related but subtly different meanings depending on context:

* In bacteria, a promoter is a cis-acting DNA sequence near the transcription start site of a gene or operon that binds to bacterial RNA polymerase. * In eukaryotes, the formal definition of a promoter (also called a basal promoter) is a RNA mutationsplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant. affect the $lacY$ and $lacA$ genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) as well.

Another type of uninducibleplugin-autotooltip__default plugin-autotooltip_bigUninducible: a mutant state wherein normally inducible genes are no longer inducible (and in fact may no longer be expressed at all). mutationplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant. is in $lacI$, where a Lac repressor proteinplugin-autotooltip__default plugin-autotooltip_bigLacI: the protein encoded by the $lacI$ gene; also called the Lac repressor protein. Binds to lactose or IPTG; upon binding, it loses the ability to bind to $lacO$. is formed that binds to the $lacO$ operatorplugin-autotooltip__default plugin-autotooltip_bigOperator: in bacterial genetics, an operator is a cis-acting genetic element that negatively regulates the expression of nearby genes. $lacO$ of the Lac operon is an example of an operator. DNAplugin-autotooltip__default plugin-autotooltip_bigDNA: deoxyribonucleic acid. The genetic material for nearly all life on Earth. but does not bind inducerplugin-autotooltip__default plugin-autotooltip_bigInducer: a molecule that triggers the expression of a gene or genes. Examples in E. coli include lactose and IPTG, which induce expression of the Lac operon in E. coli, and maltose, which induces expression of the Mal operon. An example in yeast is galactose, which induces expression of Gal genes.. These so-called “super repressorplugin-autotooltip__default plugin-autotooltip_bigRepressor: a DNA binding protein that binds to negatively acting cis-acting elements such as operators in bacteria to inhibit transcription. Compare to negative regulator.” mutationsplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant. are designated as $lacI^s$ (Table 6). Finding uninducibleplugin-autotooltip__default plugin-autotooltip_bigUninducible: a mutant state wherein normally inducible genes are no longer inducible (and in fact may no longer be expressed at all). mutationsplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant. in a regulatory geneplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) such as $lacI$ suggests the possibility that there might be positive regulatory mechanisms for geneplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) expressionplugin-autotooltip__default plugin-autotooltip_bigExpression: a term used to describe the idea that the function of a gene is apparent and can be observed. Genes may not always be expressed all the time in all places. in other genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-).

We will next consider how a different E. coliplugin-autotooltip__default plugin-autotooltip_bigEscherichia coli: an enteric bacterium used both as a model organism and as a utility organism in genetics research. E. coli is commonly used to host various cloning vectors, such as plasmids, cosmids, F factors, and bacterial artificiak chromosomes (BACs). operonplugin-autotooltip__default plugin-autotooltip_bigOperon: two or more genes that are transcribed together on an mRNA from a single promoter. Most commonly seen in bacteria; very rare in eukaryotes. is regulated positively. The Mal operonplugin-autotooltip__default plugin-autotooltip_bigMal operon: an operon in E. coli that includes the cis-acting elements of a promoter and an intiator, and the protein coding genes $malP$ and $malQ$. The Mal operon is an example of a positively-regulated operon. encodes several genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) necessary to take up and degrade maltose, a disaccharide composed of two glucose residues (Fig. 4).

Much like the Lac operonplugin-autotooltip__default plugin-autotooltip_bigLac operon: an operon in E. coli that contains the cis-acting regulatory elements $lacP$ and $lacO$, and the protein coding genes $lacZ$, $lacY$, and $lacA$. The Lac operon is an example of a negatively-regulated operon., the products of the Mal operonplugin-autotooltip__default plugin-autotooltip_bigMal operon: an operon in E. coli that includes the cis-acting elements of a promoter and an intiator, and the protein coding genes $malP$ and $malQ$. The Mal operon is an example of a positively-regulated operon. are inducedplugin-autotooltip__default plugin-autotooltip_bigInducible: a term describing a pattern of gene expression, wherein genes or operons are not expressed until some kind of condition is met, e.g., inducer is present. Not all genes are naturally inducible; some genes are naturally constitutive. when maltose is added to cells. Thus, maltose acts as an inducerplugin-autotooltip__default plugin-autotooltip_bigInducer: a molecule that triggers the expression of a gene or genes. Examples in E. coli include lactose and IPTG, which induce expression of the Lac operon in E. coli, and maltose, which induces expression of the Mal operon. An example in yeast is galactose, which induces expression of Gal genes. (Fig. 5).

When mutantsplugin-autotooltip__default plugin-autotooltip_bigMutant: an individual that has a different phenotype than wildtype and likely contains one more mutations that cause this difference. that affected the regulation of the Mal operonplugin-autotooltip__default plugin-autotooltip_bigMal operon: an operon in E. coli that includes the cis-acting elements of a promoter and an intiator, and the protein coding genes $malP$ and $malQ$. The Mal operon is an example of a positively-regulated operon. were isolated, the most common type consisted of uninducibleplugin-autotooltip__default plugin-autotooltip_bigUninducible: a mutant state wherein normally inducible genes are no longer inducible (and in fact may no longer be expressed at all). mutationsplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant. in a geneplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) known as $malT$. We can apply dominanceplugin-autotooltip__default plugin-autotooltip_bigDominant: used to describe an allele, usually in comparison to wildtype. Dominant alleles will express their phenotype when combined with a wildtype allele. tests and cisplugin-autotooltip__default plugin-autotooltip_bigCis and trans: In genetics, cis and trans are terms used to describe the relative physical locations of genes or genetic elements. If two genes are in cis, this means that they are physically located on the same DNA molecule. If two genes are in trans, this means that they are physically located on two different/transplugin-autotooltip__default plugin-autotooltip_bigCis and trans: In genetics, cis and trans are terms used to describe the relative physical locations of genes or genetic elements. If two genes are in cis, this means that they are physically located on the same DNA molecule. If two genes are in trans, this means that they are physically located on two different tests we just learned earlier in this chapter to $malT$ mutationsplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant.. We obtain the following results:

From Table 7, it looks as if the $malT^-$ trait is not expressedplugin-autotooltip__default plugin-autotooltip_bigExpression: a term used to describe the idea that the function of a gene is apparent and can be observed. Genes may not always be expressed all the time in all places. either in cisplugin-autotooltip__default plugin-autotooltip_bigCis and trans: In genetics, cis and trans are terms used to describe the relative physical locations of genes or genetic elements. If two genes are in cis, this means that they are physically located on the same DNA molecule. If two genes are in trans, this means that they are physically located on two different or in transplugin-autotooltip__default plugin-autotooltip_bigCis and trans: In genetics, cis and trans are terms used to describe the relative physical locations of genes or genetic elements. If two genes are in cis, this means that they are physically located on the same DNA molecule. If two genes are in trans, this means that they are physically located on two different (compare to $lacI^{-d}$). Because $malT^-$ is recessiveplugin-autotooltip__default plugin-autotooltip_bigRecessive: used to describe an allele, usually in comparison to wildtype. Recessive alleles do not exhibit their phenotype when combined with a wildtype allele., it makes more sense to consider the properties of the dominantplugin-autotooltip__default plugin-autotooltip_bigDominant: used to describe an allele, usually in comparison to wildtype. Dominant alleles will express their phenotype when combined with a wildtype allele. $malT^+$ alleleplugin-autotooltip__default plugin-autotooltip_bigAllele: a version of a gene. Alleles of a gene are different if they have differences in their DNA sequence. in the cisplugin-autotooltip__default plugin-autotooltip_bigCis and trans: In genetics, cis and trans are terms used to describe the relative physical locations of genes or genetic elements. If two genes are in cis, this means that they are physically located on the same DNA molecule. If two genes are in trans, this means that they are physically located on two different/transplugin-autotooltip__default plugin-autotooltip_bigCis and trans: In genetics, cis and trans are terms used to describe the relative physical locations of genes or genetic elements. If two genes are in cis, this means that they are physically located on the same DNA molecule. If two genes are in trans, this means that they are physically located on two different test. Viewed in this way, the $malT^+$ trait is expressedplugin-autotooltip__default plugin-autotooltip_bigExpression: a term used to describe the idea that the function of a gene is apparent and can be observed. Genes may not always be expressed all the time in all places. in both cisplugin-autotooltip__default plugin-autotooltip_bigCis and trans: In genetics, cis and trans are terms used to describe the relative physical locations of genes or genetic elements. If two genes are in cis, this means that they are physically located on the same DNA molecule. If two genes are in trans, this means that they are physically located on two different and transplugin-autotooltip__default plugin-autotooltip_bigCis and trans: In genetics, cis and trans are terms used to describe the relative physical locations of genes or genetic elements. If two genes are in cis, this means that they are physically located on the same DNA molecule. If two genes are in trans, this means that they are physically located on two different and therefore $malT$ is considered to be transplugin-autotooltip__default plugin-autotooltip_bigCis and trans: In genetics, cis and trans are terms used to describe the relative physical locations of genes or genetic elements. If two genes are in cis, this means that they are physically located on the same DNA molecule. If two genes are in trans, this means that they are physically located on two different-acting.

This behavior is different from any of the Lac mutationsplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant. that we have discussed. The interpretation of this data is that $malT$ encodes a diffusible gene productplugin-autotooltip__default plugin-autotooltip_bigGene product: the molecule that is produced based on information contained within a gene and provides function to the organism. Most of the time, a gene product is a protein. Sometimes gene products can also be an RNA molecule. In forward genetic analysis, we can't formally tell if a gene product is (not a sequenceplugin-autotooltip__default plugin-autotooltip_bigSequence: the precise order of monomers in a polymer. In DNA, it refers to the order of G, A, T, and C nucleotides. In RNA, it refers to the order of G, A, U, and C nucleotides. In proteins, it refers to the order of amino acids./site on DNAplugin-autotooltip__default plugin-autotooltip_bigDNA: deoxyribonucleic acid. The genetic material for nearly all life on Earth.) that is required for activation of transcriptionplugin-autotooltip__default plugin-autotooltip_bigRNA transcription: the process of RNA polymerase using the DNA sequence of a gene as a template to form an mRNA (in prokaryotes) or pre-mRNA (in eukaryotes). In most cases, “transcription” implies RNA transcription. of the Mal operonplugin-autotooltip__default plugin-autotooltip_bigMal operon: an operon in E. coli that includes the cis-acting elements of a promoter and an intiator, and the protein coding genes $malP$ and $malQ$. The Mal operon is an example of a positively-regulated operon.. Unlike the LacIplugin-autotooltip__default plugin-autotooltip_bigLacI: the protein encoded by the $lacI$ gene; also called the Lac repressor protein. Binds to lactose or IPTG; upon binding, it loses the ability to bind to $lacO$. proteinplugin-autotooltip__default plugin-autotooltip_bigProtein: a molecule that is formed by the translation of messenger RNAs (mRNAs). Functions that proteins provide are what usually give organisms their phenotypes., which is a tetramer (a proteinplugin-autotooltip__default plugin-autotooltip_bigProtein: a molecule that is formed by the translation of messenger RNAs (mRNAs). Functions that proteins provide are what usually give organisms their phenotypes. formed from 4 identical polypeptide subunits), the MalTplugin-autotooltip__default plugin-autotooltip_bigMalT: a protein encoded by the $malT$ gene that acts as a transactivator for the Mal operon. proteinplugin-autotooltip__default plugin-autotooltip_bigProtein: a molecule that is formed by the translation of messenger RNAs (mRNAs). Functions that proteins provide are what usually give organisms their phenotypes. functions as a monomer. Genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) with functions like malT are usually called an activatorplugin-autotooltip__default plugin-autotooltip_bigTransactivator (activator): a DNA binding protein that binds to promoter sequences to activate the transcription of nearby genes. In the context of gene expression, “activator” is usually a synonym for transactivator. Compare with positive regulator. (also called a transactivatorplugin-autotooltip__default plugin-autotooltip_bigTransactivator (activator): a DNA binding protein that binds to promoter sequences to activate the transcription of nearby genes. In the context of gene expression, “activator” is usually a synonym for transactivator. Compare with positive regulator.). As shown in Fig. 6, maltose binds to the MalTplugin-autotooltip__default plugin-autotooltip_bigMalT: a protein encoded by the $malT$ gene that acts as a transactivator for the Mal operon. activatorplugin-autotooltip__default plugin-autotooltip_bigTransactivator (activator): a DNA binding protein that binds to promoter sequences to activate the transcription of nearby genes. In the context of gene expression, “activator” is usually a synonym for transactivator. Compare with positive regulator. proteinplugin-autotooltip__default plugin-autotooltip_bigProtein: a molecule that is formed by the translation of messenger RNAs (mRNAs). Functions that proteins provide are what usually give organisms their phenotypes., which causes a conformational change in MalTplugin-autotooltip__default plugin-autotooltip_bigMalT: a protein encoded by the $malT$ gene that acts as a transactivator for the Mal operon. and allows it to bind near to the promoterplugin-autotooltip__default plugin-autotooltip_bigPromoter: has multiple closely related but subtly different meanings depending on context:

* In bacteria, a promoter is a cis-acting DNA sequence near the transcription start site of a gene or operon that binds to bacterial RNA polymerase. * In eukaryotes, the formal definition of a promoter (also called a basal promoter) is a RNA and to stimulate transcriptionplugin-autotooltip__default plugin-autotooltip_bigRNA transcription: the process of RNA polymerase using the DNA sequence of a gene as a template to form an mRNA (in prokaryotes) or pre-mRNA (in eukaryotes). In most cases, “transcription” implies RNA transcription.. Note that the genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) required for maltose uptake are located in an operonplugin-autotooltip__default plugin-autotooltip_bigOperon: two or more genes that are transcribed together on an mRNA from a single promoter. Most commonly seen in bacteria; very rare in eukaryotes. elsewhere on the chromosomeplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins., but these genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) are also regulated by MalTplugin-autotooltip__default plugin-autotooltip_bigMalT: a protein encoded by the $malT$ gene that acts as a transactivator for the Mal operon..

In this model, a DNAplugin-autotooltip__default plugin-autotooltip_bigDNA: deoxyribonucleic acid. The genetic material for nearly all life on Earth. site called the initiatorplugin-autotooltip__default plugin-autotooltip_bigInitiator: in bacterial genetics, an initiator is a cis-acting element that positively regulates the expression of a target gene or operon. is where the MalTplugin-autotooltip__default plugin-autotooltip_bigMalT: a protein encoded by the $malT$ gene that acts as a transactivator for the Mal operon. activatorplugin-autotooltip__default plugin-autotooltip_bigTransactivator (activator): a DNA binding protein that binds to promoter sequences to activate the transcription of nearby genes. In the context of gene expression, “activator” is usually a synonym for transactivator. Compare with positive regulator. proteinplugin-autotooltip__default plugin-autotooltip_bigProtein: a molecule that is formed by the translation of messenger RNAs (mRNAs). Functions that proteins provide are what usually give organisms their phenotypes. binds, near the promoterplugin-autotooltip__default plugin-autotooltip_bigPromoter: has multiple closely related but subtly different meanings depending on context:

* In bacteria, a promoter is a cis-acting DNA sequence near the transcription start site of a gene or operon that binds to bacterial RNA polymerase. * In eukaryotes, the formal definition of a promoter (also called a basal promoter) is a RNA to activate transcriptionplugin-autotooltip__default plugin-autotooltip_bigRNA transcription: the process of RNA polymerase using the DNA sequence of a gene as a template to form an mRNA (in prokaryotes) or pre-mRNA (in eukaryotes). In most cases, “transcription” implies RNA transcription.. If you think about how mutationsplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant. in an initiatorplugin-autotooltip__default plugin-autotooltip_bigInitiator: in bacterial genetics, an initiator is a cis-acting element that positively regulates the expression of a target gene or operon. site should behave in dominanceplugin-autotooltip__default plugin-autotooltip_bigDominant: used to describe an allele, usually in comparison to wildtype. Dominant alleles will express their phenotype when combined with a wildtype allele. and cisplugin-autotooltip__default plugin-autotooltip_bigCis and trans: In genetics, cis and trans are terms used to describe the relative physical locations of genes or genetic elements. If two genes are in cis, this means that they are physically located on the same DNA molecule. If two genes are in trans, this means that they are physically located on two different/transplugin-autotooltip__default plugin-autotooltip_bigCis and trans: In genetics, cis and trans are terms used to describe the relative physical locations of genes or genetic elements. If two genes are in cis, this means that they are physically located on the same DNA molecule. If two genes are in trans, this means that they are physically located on two different tests, you will see why in practice it is difficult to distinguish initiatorplugin-autotooltip__default plugin-autotooltip_bigInitiator: in bacterial genetics, an initiator is a cis-acting element that positively regulates the expression of a target gene or operon. site mutationsplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant. from promoterplugin-autotooltip__default plugin-autotooltip_bigPromoter: has multiple closely related but subtly different meanings depending on context:

* In bacteria, a promoter is a cis-acting DNA sequence near the transcription start site of a gene or operon that binds to bacterial RNA polymerase. * In eukaryotes, the formal definition of a promoter (also called a basal promoter) is a RNA mutationsplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant. (compare to $lacP$ and $lacO$ mutationsplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant., where there are genetic tests that can distinguish between them).

It is also possible to isolate “super activatorplugin-autotooltip__default plugin-autotooltip_bigTransactivator (activator): a DNA binding protein that binds to promoter sequences to activate the transcription of nearby genes. In the context of gene expression, “activator” is usually a synonym for transactivator. Compare with positive regulator.” $malT$ mutantsplugin-autotooltip__default plugin-autotooltip_bigMutant: an individual that has a different phenotype than wildtype and likely contains one more mutations that cause this difference. that will bind to the initiatorplugin-autotooltip__default plugin-autotooltip_bigInitiator: in bacterial genetics, an initiator is a cis-acting element that positively regulates the expression of a target gene or operon. site and activate transcriptionplugin-autotooltip__default plugin-autotooltip_bigRNA transcription: the process of RNA polymerase using the DNA sequence of a gene as a template to form an mRNA (in prokaryotes) or pre-mRNA (in eukaryotes). In most cases, “transcription” implies RNA transcription. regardless of whether the inducerplugin-autotooltip__default plugin-autotooltip_bigInducer: a molecule that triggers the expression of a gene or genes. Examples in E. coli include lactose and IPTG, which induce expression of the Lac operon in E. coli, and maltose, which induces expression of the Mal operon. An example in yeast is galactose, which induces expression of Gal genes. maltose is present. Such allelesplugin-autotooltip__default plugin-autotooltip_bigAllele: a version of a gene. Alleles of a gene are different if they have differences in their DNA sequence. of the $malT$ geneplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) are called $malT^c$ and their properties are given in Table 8.

Exercise 1: (Challenge question!) You isolate an E. coliplugin-autotooltip__default plugin-autotooltip_bigEscherichia coli: an enteric bacterium used both as a model organism and as a utility organism in genetics research. E. coli is commonly used to host various cloning vectors, such as plasmids, cosmids, F factors, and bacterial artificiak chromosomes (BACs). mutantplugin-autotooltip__default plugin-autotooltip_bigMutant: an individual that has a different phenotype than wildtype and likely contains one more mutations that cause this difference. that is auxotrophicplugin-autotooltip__default plugin-autotooltip_bigAuxotroph: a mutant that cannot synthesize one more essential nutrient from minimal media needed for survival or proliferation. for raffinose, a trisaccharide comprised of galactose (a monosaccharide) and fructose (a disaccharide). You temporarily name this mutantplugin-autotooltip__default plugin-autotooltip_bigMutant: an individual that has a different phenotype than wildtype and likely contains one more mutations that cause this difference. $rafA$. In biochemical experiments you find that $rafA$ mutantsplugin-autotooltip__default plugin-autotooltip_bigMutant: an individual that has a different phenotype than wildtype and likely contains one more mutations that cause this difference. do not express α-galactosidase, an enzymeplugin-autotooltip__default plugin-autotooltip_bigEnzyme: a macromolecule, usually a protein (but sometimes an RNA), that functions as a catalyst of some kind of biochemical reaction. required to metabolize raffinose, and that in wildtypeplugin-autotooltip__default plugin-autotooltip_bigWildtype: a reference strain of an organism that scientists operationally define as “normal” to which mutants are compared. Not to be confused with wild organisms. E. coliplugin-autotooltip__default plugin-autotooltip_bigEscherichia coli: an enteric bacterium used both as a model organism and as a utility organism in genetics research. E. coli is commonly used to host various cloning vectors, such as plasmids, cosmids, F factors, and bacterial artificiak chromosomes (BACs)., α-galactosidase expressionplugin-autotooltip__default plugin-autotooltip_bigExpression: a term used to describe the idea that the function of a gene is apparent and can be observed. Genes may not always be expressed all the time in all places. is inducedplugin-autotooltip__default plugin-autotooltip_bigInducible: a term describing a pattern of gene expression, wherein genes or operons are not expressed until some kind of condition is met, e.g., inducer is present. Not all genes are naturally inducible; some genes are naturally constitutive. by raffinose. What experiments would you do to find out if $rafA$ codes for a metabolic enzymeplugin-autotooltip__default plugin-autotooltip_bigEnzyme: a macromolecule, usually a protein (but sometimes an RNA), that functions as a catalyst of some kind of biochemical reaction. vs a regulatory geneplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-)?

Conceptual question: With regards to the Mal operonplugin-autotooltip__default plugin-autotooltip_bigMal operon: an operon in E. coli that includes the cis-acting elements of a promoter and an intiator, and the protein coding genes $malP$ and $malQ$. The Mal operon is an example of a positively-regulated operon., it should also be possible to isolate dominant negativeplugin-autotooltip__default plugin-autotooltip_bigAntimorphic mutation: A mutation that, when combined with a wildtype allele (either as a merodiploid or as a diploid), the total amount of activity is less than wildtype. The implication is that the gene product produced by the antimorphic allele interferes with the function of the wildtype gene product. Also called a dominant negative allele. $malT$ mutantsplugin-autotooltip__default plugin-autotooltip_bigMutant: an individual that has a different phenotype than wildtype and likely contains one more mutations that cause this difference. that will interfere with the function of the $malT^+$ wildplugin-autotooltip__default plugin-autotooltip_bigWild: refers to organisms that grow in wild populations. Not to be confused with wildtype. type alleleplugin-autotooltip__default plugin-autotooltip_bigAllele: a version of a gene. Alleles of a gene are different if they have differences in their DNA sequence. in a merodiploidplugin-autotooltip__default plugin-autotooltip_bigMerodiploid: used to describe an organism that is naturally haploid but is partially diploid for a portion of its genome due to the presence of an episome that contains a chromosomal fragment.. However, $malT^{-d}$ dominant negativeplugin-autotooltip__default plugin-autotooltip_bigAntimorphic mutation: A mutation that, when combined with a wildtype allele (either as a merodiploid or as a diploid), the total amount of activity is less than wildtype. The implication is that the gene product produced by the antimorphic allele interferes with the function of the wildtype gene product. Also called a dominant negative allele. mutantsplugin-autotooltip__default plugin-autotooltip_bigMutant: an individual that has a different phenotype than wildtype and likely contains one more mutations that cause this difference. have not been isolated. By comparison, dominant negativeplugin-autotooltip__default plugin-autotooltip_bigAntimorphic mutation: A mutation that, when combined with a wildtype allele (either as a merodiploid or as a diploid), the total amount of activity is less than wildtype. The implication is that the gene product produced by the antimorphic allele interferes with the function of the wildtype gene product. Also called a dominant negative allele. $lacI$ mutantsplugin-autotooltip__default plugin-autotooltip_bigMutant: an individual that has a different phenotype than wildtype and likely contains one more mutations that cause this difference. have been isolated (see Table 4). Why do you think this is? How do you think dominant negativeplugin-autotooltip__default plugin-autotooltip_bigAntimorphic mutation: A mutation that, when combined with a wildtype allele (either as a merodiploid or as a diploid), the total amount of activity is less than wildtype. The implication is that the gene product produced by the antimorphic allele interferes with the function of the wildtype gene product. Also called a dominant negative allele. mutationsplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant. work at the biochemical (proteinplugin-autotooltip__default plugin-autotooltip_bigProtein: a molecule that is formed by the translation of messenger RNAs (mRNAs). Functions that proteins provide are what usually give organisms their phenotypes.) level? An important hint is that LacIplugin-autotooltip__default plugin-autotooltip_bigLacI: the protein encoded by the $lacI$ gene; also called the Lac repressor protein. Binds to lactose or IPTG; upon binding, it loses the ability to bind to $lacO$. functions as a tetrameric proteinplugin-autotooltip__default plugin-autotooltip_bigProtein: a molecule that is formed by the translation of messenger RNAs (mRNAs). Functions that proteins provide are what usually give organisms their phenotypes. whereas MalTplugin-autotooltip__default plugin-autotooltip_bigMalT: a protein encoded by the $malT$ gene that acts as a transactivator for the Mal operon. functions as a monomer. This is a very useful discussion to have because it reinforces the concept of the relationship between genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) and genetic descriptions of mutationsplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant., and physical manifestations of phenotypesplugin-autotooltip__default plugin-autotooltip_bigPhenotype: an observable feature or property of an organism. by way of the products of genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) (i.e., proteinsplugin-autotooltip__default plugin-autotooltip_bigProtein: a molecule that is formed by the translation of messenger RNAs (mRNAs). Functions that proteins provide are what usually give organisms their phenotypes.).