Question

1. You have identified a mutation in Drosophila that prevents the polyadenylation of the 3′ end of the RNA transcript. However, much to your surprise, all the enzymes required for polyadenylation are normal. You determine that the mutation is, instead, in one of the subunits of RNA polymerase II. Which subunit is mutant and how does this mutation result in failure to add a polyA tail to the RNA?

Answer 1

As the mutation have been found to be associated with RNA pol II, it can said that the domain of RNA pol II involved in polyadenylation has the mutation. Carboxy terminal domain (CTD) of large sub unit of RNA pol II is responsible for polyadenylation. Thus, the mutation is in this region.

CTD of large sub unit of RNA pol II has a consensus sequence of Tyr-Ser-Pro-Thr-Ser-Pro-Ser, present in multiple numbers in the domain. This heptapeptide sequence is thought to be responsible for many functions. Like, phosphorylation in 2nd Serine and 5th serine residue is thought to be responsible for its polyadenylation. Phosphated 2nd serine is recruits or assembles the polyadenylation complex.This mutation might have changed these residues leading to failure in polyadenylation.

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