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 system or 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.

Please give more information that ties in replication of viruses with RNA genomes, and how the virus replication not being inhibited by actinomycin D plays a role too.

Answer 1

Virus enters a cell through fusion and transduction.

• In fusion - viral receptors present on the viral envelope attaches to cell receptors of the host. then by activting secondary messengers it gain entry into the host cell.
• in transduction- viral genome is intoduced into the host cell by virus itself or by viral vector.

How viral genome replicates in a host cell:-

• In generalised transduction- 1. virus interacts with the host cell and release of viral genome into host cell. 2. the viral genome got integrated into host genome 3. Integration of viral genome causes excision of host genome into several small fragments. 4. synthesising of viral coat proteins and viral genome replication. 5. release by lytic phase.
• In specialised transduction - 1.virus infects the host cell by realease of viral genome 2. viral genome integrates into host genome. 3.imprecise excision ( some host chromosome also got included along with prophage) 4. release of new viral particle

Action of actinomycin D:-

• It works by inhibiting RNA synthesis.
• it will not affect RNA replication directly.
• it binds to DNA template thus inhibiting its action with RNA polymerase.

Why virus replication is not inhibited by actinomycin D:-

• Due to inhibition of DNA dependent RNA polymerase of host cell shortly after infection with the virus and formation of new RNA dependent RNA polymerase.
• the formation of this virus specific RNA synthesising system in the cytoplasm of host cell caused non inhibition by actinomycin D.