Question

Explain Both

a) Picornaviruses are famous for their use of protein processing in gene expression. What are two other groups of viruses (non-picorna) that rely on protein processing and why should protein processing be so prevalent? In other words, what are its advantages?

b) Both TMV and BMV rely on subgenomic mRNAs to help control gene expression but the two viruses have very different ways of utilizing their sgRNAs. Explain the difference.

Answer 1

a)Picrornaviruses produce a single large polyprotein upon translation, which has multiple mature polypeptides hich inturn is cleaved by viral or cellular proteases.Many other viruses also produce proteins in a smilar way by protein processing.This presents several advantages like condensation of genetic material ;additonal elements like promoters or enahncers not required for every protein, proper regulation of protein activity depending upon where it has to be cleaved.Protein precursors can serve different functions as compared to their mature forms.

Retroviruses like HIV also process proteins in gene expression, as well as Alphaviruses.

b) BMV or Brome Mosiac Virus contains three different RNAs strands whereas TMV of Tobacco Mosiac Virus contains a single RNA strand.TMV makes sgRNA via internal initiation, whereas BMV does not.BMV has sgRNA that are 3'-coterminal with viral genomic RNA.There is different cis-signal regulation in both TMV and BMV.