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Ch. 16 - Regulation of Gene Expression in Bacteria
Klug - Concepts of Genetics 12th Edition
Klug12th EditionConcepts of Genetics ISBN: 9780135564776Not the one you use?Change textbook
All textbooksKlug 12th EditionCh. 16 - Regulation of Gene Expression in BacteriaProblem 10
Chapter 16, Problem 10

Predict the effect on the inducibility of the lac operon of a mutation that disrupts the function of:
(a) The CRP gene, which encodes the CAP protein
(b) The CAP-binding site within the promoter.

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1
Step 1: Understand the role of the CRP gene and CAP protein in the lac operon. The CRP gene encodes the CAP protein, which acts as a positive regulator by binding to the CAP-binding site near the lac promoter to enhance transcription when glucose levels are low.
Step 2: For part (a), analyze the effect of a mutation that disrupts the CRP gene function. Without functional CAP protein, the positive regulation of the lac operon is lost, so even when lactose is present and glucose is low, the operon induction will be reduced.
Step 3: For part (b), consider the mutation in the CAP-binding site within the promoter. Even if CAP protein is present, it cannot bind to the promoter to stimulate transcription, leading to a similar reduction in inducibility as in part (a).
Step 4: Compare the effects of both mutations on lac operon inducibility. Both mutations impair the positive regulation by CAP, so the lac operon will have lower expression levels in the presence of lactose and absence of glucose compared to the wild type.
Step 5: Summarize that the inducibility of the lac operon depends on CAP binding to its site; disruption of either the CAP protein or its binding site reduces the operon's ability to be induced efficiently.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Lac Operon Regulation

The lac operon is a set of genes involved in lactose metabolism in E. coli, regulated by proteins that respond to environmental signals. Its expression is controlled by the presence or absence of lactose and glucose, allowing the cell to efficiently use available sugars.
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Lac Operon Regulation

Role of CAP (Catabolite Activator Protein)

CAP is a regulatory protein that, when bound to cAMP, enhances transcription of the lac operon by facilitating RNA polymerase binding. It acts as an activator in low-glucose conditions, increasing operon inducibility by promoting gene expression.
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Proteins

CAP-Binding Site Function

The CAP-binding site is a specific DNA sequence near the lac promoter where the CAP-cAMP complex binds. This binding is essential for the positive regulation of the lac operon, as it helps recruit RNA polymerase and increases transcription efficiency.
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Functional Genomics
Related Practice
Textbook Question

The locations of numerous lacI⁻ and lacIˢ mutations have been determined within the DNA sequence of the lacI gene. Among these, lacI⁻ mutations were found to occur in the 5′-upstream region of the gene, while lacIˢ mutations were found to occur farther downstream in the gene. Are the locations of the two types of mutations within the gene consistent with what is known about the function of the repressor that is the product of the lacI gene?

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Textbook Question

Describe the experimental rationale that allowed the lac repressor to be isolated.

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Textbook Question

What properties demonstrate that the lac repressor is a protein? Describe the evidence that it indeed serves as a repressor within the operon system.

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Textbook Question

Erythritol, a natural sugar abundant in fruits and fermenting foods, is about 65 percent as sweet as table sugar and has about 95 percent fewer calories. It is 'tooth friendly' and generally devoid of negative side effects as a human consumable product. Pathogenic Brucella strains that catabolize erythritol contain four closely spaced genes, all involved in erythritol metabolism. One of the four genes (eryD) encodes a product that represses the expression of the other three genes. Erythritol catabolism is stimulated by erythritol. Present a simple regulatory model to account for the regulation of erythritol catabolism in Brucella. Does this system appear to be under inducible or repressible control?

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Textbook Question

Describe the role of attenuation in the regulation of tryptophan biosynthesis.

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Textbook Question
Attenuation of the trp operon was viewed as a relatively inefficient way to achieve genetic regulation when it was first discovered in the 1970s. Since then, however, attenuation has been found to be a relatively common regulatory strategy. Assuming that attenuation is a relatively inefficient way to achieve genetic regulation, what might explain its widespread occurrence?
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