Need help solving thank you in advance! A fictional bacterial operon is responsi

Question

Need help solving thank you in advance! A fictional bacterial operon is responsible for the production of the biosynthetic enzymes needed to make the theoretical amino acid Tisophane (Tis). In the wild? type condition, when Tis is present, no enzymes are made. In the absence of Tis, the enzymes are made. The operon is regulated by a separate gene, R, deletion of which causes loss of enzyme production, regardless of whether Tis is present. A second class of regulatory mutations has been identified and these map to a region (the RB site) near the promoter of the Tis operon; these so? called RB? mutations also block production of the enzymes, regardless of the availability of Tis. Is the operon under positive or negative control? Justify your answer. Propose a model for regulation of the operon which explains the lack of enzyme production in the presence of Tis in wildtype cells, the role of the R protein and the effects of the RB? mutations.

Explanation / Answer

b.

In this model four things are involved: 1) activator 2) repressor 3) co-repressor and 4) a regulatory region, which are denoted by

R -------- activator

B -------- repressor

Tis ------- co-repressor

RB -------- regulatory region (operator) having binding sites for R and B

This model highlights that Tis / B complex inhibits the transcription of Tis enzymes by binding to the B region of RB operator. The presence of R protein decreases the affinity of Tis / B complex to B region of RB. R protein binds to R region on RB and causes a conformation change in B region. The change in conformation of B region decreases affinity of Tis / B complex.

So, when R gene is absent, Tis / B complex bind tightly to the RB site and inhibit the transcription.

Secondly, when R site is mutated in RB, R protein can't bind which in turn doesn't displace the Tis / B complex and thus inhibition of transcription.

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