Question

1. Suppose that you isolated an enveloped icosahedral RNA virus.  Purified RNA from this virus is capable of supporting translation in a rabbit reticulocyte cell‑free translation systemor in any other such system. Further analysis indicates that this virus replication is not inhibited by actinomycin D, a strong inhibitor of DNA-dependent RNA polymerase.Based on this information, discuss the mechanism by which this virus replicates its genome in infected susceptible, permissive cells.

2. Suppose that you isolated an enveloped helical RNA virus. Purified RNA from this virus is capable of supporting translation in a rabbit reticulocyte cell‑free translation systemor in any other such system  Further analysis indicates that this virus replication is inhibited if infected cells are incubated with protease inhibitor such as trypsin inhibitor. Based on this information, discuss the mechanism by which this virus replicates its genome in infected susceptible, permissive cells.

Answer 1

1.

Actinomycin D is an inhibitor of cellular RNA polymerase. Since, the viral replication is not inhibited it means that the virus carries its own RNA polymerase which is not inhibited by actinomycin D

Vesicular Stomatitis virus (VSV) is such an example. It has a bullet shaped capsid, is enveloped and carries a 11 Kb negative sense RNA .

It encodes for 5 protein - nuceloprotein, matrix protein, surface protein, structural protein, RNA deoendepnt RNA polymerase.

All transcript have a 5' cap and a 3' tail.

A single RNA pol binds to transcribes the + RNA strand from the negative sense RNA. At the termination signal of each transcript the RNA polymerase stutters and so adds several A repeatedly.

As the transcripts are synthesized, N protein (nucleoprotein) accumulates. It associates with mRNA as its transcribed which reduces stuttering.

This mRNA does not have a polyA tail and so serves as a template for synthesis of negative sense RNA.