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Ch. 16 - Regulation of Gene Expression in Bacteria
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All textbooksKlug 12th EditionCh. 16 - Regulation of Gene Expression in BacteriaProblem 24

Chapter 16, Problem 24

Figure 16.13 depicts numerous critical regions of the leader sequence of mRNA that play important roles during the process of attenuation in the trp operon. A closer view of the leader sequence, which begins at about position 30 downstream from the 5' end, is shown below, running along both columns. Within this molecule are the sequences that cause the formation of the alternative hairpins. It also contains the successive triplets that encode tryptophan, where stalling during translation occurs. Take a large piece of paper (such as manila wrapping paper) and, along with several other students from your genetics class, work through the base sequence to identify the trp codons and the parts of the molecule representing the base-pairing regions that form the terminator and antiterminator hairpins shown in Figure 16.13.

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Hello everyone here. We have a question asking us, how does transcription continuation prevent proper transcription and when the attenuate ER is present in the D. N. A sequence, it results in the formation of an m r n. A stem loop that prevents further transcription. And because this is non functional RNA proper transcription is prevented. So our answer is C. The attenuate er forms an M. RNA stem loop that prevents the transcription. Thank you for watching. Bye!
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Textbook Question
A bacterial operon is responsible for the production of the biosynthetic enzymes needed to make the hypothetical amino acid tisophane (tis). The operon is regulated by a separate gene, R. The deletion of R causes the loss of enzyme synthesis. In the wild-type condition, when tis is present, no enzymes are made; in the absence of tis, the enzymes are made. Mutations in the operator gene (O⁻) result in repression regardless of the presence of tis. Is the operon under positive or negative control? Propose a model for (a) repression of the genes in the presence of tis in wild-type cells and (b) the mutations.
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Textbook Question
A marine bacterium is isolated and shown to contain an inducible operon whose genetic products metabolize oil when it is encountered in the environment. Investigation demonstrates that the operon is under positive control and that there is a reg gene whose product interacts with an operator region (o) to regulate the structural genes, designated sg. In an attempt to understand how the operon functions, a constitutive mutant strain and several partial diploid strains were isolated and tested with the results shown in the following table. Host Chromosome F' Factor Phenotype Wild type None Inducible Wild type reg gene from mutant strain Inducible Wild type Operon from mutant strain Constitutive Mutant strain reg gene from wild type Constitutive Draw all possible conclusions about the mutation as well as the nature of regulation of the operon. Is the constitutive mutation in the trans-acting reg element or in the cis-acting o operator element?
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Textbook Question
The SOS repair genes in E. coli (discussed in Chapter 15) are negatively regulated by the lexA gene product, called the LexA repressor. When a cell's DNA sustains extensive damage, the LexA repressor is inactivated by the recA gene product (RecA), and transcription of the SOS genes is increased dramatically. One of the SOS genes is the uvrA gene. You are a student studying the function of the uvrA gene product in DNA repair. You isolate a mutant strain that shows constitutive expression of the UvrA protein. Naming this mutant strain uvrAᶜ, you construct the diagram shown above in the right-hand column showing the lexA and uvrA operons: Describe two different mutations that would result in a uvrA constitutive phenotype. Indicate the actual genotypes involved. (Leader sequence for Problem 24 above)
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