Question

Using your knowledge of repression and attenuation of gene expression, in the context of the Trp operon. Answer the next two questions.

a. Give one example of how these two regulation schemes similar? (3 points)

b. Give one example of how they are different?

Explain how ⍴-independent termination is able to halt transcription of an mRNA molecule.

In the maturation of eukaryotic mRNA, what is the role of poly-A addition? (2 points) What enzymes are involved in this reaction?

Answer 1

In repression, a repressor (Trans-acting factor) binds to the operator and inhibits the recruitment of RNA polymerase to the promoter. It is a transcriptional regulatory mechanism.

In attenuation, a sequence element (Cis-acting factor) produces a structure that inhibits the recruitment of RNA polymerase to the promoter. It is a translation-coupled regulatory mechanism.

In attenuation, there is no production of any diffusible product. A sequence element inhibits the process. In the repressor, the repressor has to be produced to inhibit transcription. Attenuator elements cannot be complemented as they act in cis. Repressor can be complemented as it is a trans-acting factor.

Rho-independent termination = Intrinsic termination
In this mechanism, the newly formed RNA can fold to form a secondary structure (GC-rich Stem-loop structure) that dissociates the RNA polymerase from the template strand.

Eukaryotic mRNA is poly-adenylated at the 3'-end. It is mediated by Poly-A polymerase (It is a template-independent polymerase). Poly-A tail is required for the stability of mRNA, nuclear export, and efficient translation.