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Chapter 22: Problem 11

The mechanism of attenuation requires the presence of a leader region. Predict the effect of the following changes on regulation of the trp operon: (a) The entire leader region is deleted. (b) The sequence encoding the leader peptide is deleted. (c) The leader region, an \(\mathrm{AUG}\) codon, is mutated.

Short Answer

Expert verified
Each change leads to a dysfunction in the attenuation mechanism of the trp operon causing it to remain active, and likely resulting in the overproduction of tryptophan.

Step by step solution

01

Scenario A: Deleting the leader region

The leader region contains sequences for a regulatory peptide that interacts with the ribosome during transcription. Without this region, the precise control of the trp operon is lost, likely leading to persistent activation and overproduction of tryptophan - as the attenuation mechanism is lost.
02

Scenario B: Deleting the sequence encoding the leader peptide

The leader peptide is critical for the attenuation mechanism. Without it, the trp operon would likely remain activated regardless of the level of tryptophan, also causing an overproduction. In other words, the inability to produce the leader peptide mimics the effect of deleting the entire leader region.
03

Scenario C: Mutation of the AUG codon in the leader region

The AUG codon in the leader region serves as the 'start' signal for synthesis of the leader peptide. Its mutation would prevent the leader peptide from being synthesized. Thus, similar to scenario B, the trp operon would be constantly active, and overproduction of tryptophan would occur.

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Most popular questions from this chapter

Polypeptide chain elongation on the ribosome can be broken down into three discrete steps (the microcycle): (1) binding of the correct aminoacyl-tRNA in the ribosome's A site, (2) peptide bond formation, and (3) translocation. What, specifically, is it that gets translocated in the third step of this cycle?

In the operons that contain genes for isoleucine biosynthesis, the leader regions that precede the genes contain multiple codons that specify not only isoleucine but valine and leucine as well. Suggest a reason why this is so.

In Chapter 21 , you learned of many different regulatory mechanisms that control transcription of the lac operon in \(E\). coli. In Chapter 22 , one of the mechanisms of translational regulation discussed was called attenuation. Would you predict that in some other bacterial species the lacoperon might have evolved such that an attenuation mechanism was used to regulate expression levels from this operon?

Given that the genetic code is universal, would a plant mRNA be correctly translated in a prokaryotic cell like E. coli?

On rare occasions, the translation machinery encounters a codon that cannot be quickly interpreted because of the lack of a particular tRNA or release factor. In these cases, the ribosome may pause and then shift by a single nucleotide and begin translating a different reading frame. Such an occurrence is known as translational frameshifting. The E. coli release factor RF-2, which is translated from mRNA that contains an internal UGA stop codon, is produced by translational frameshifting. Explain how this phenomenon might regulate RF- 2 production.
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