Question

Clearly state the difference between plus and minus stranded RNA viruses (using a nucleicacid example if needed). What special problems do minus strand RNA viruses face when they enter the cell, and how do they solve the problem? What special problems do plus strand RNA viruses have, and how do they solve the problem? Be specific.

Answer 1

1. Example: + Sense RNA viruses: Polio virus (Picorna virus).

Problem:

The RNA of Poliovirus functions like mRNA but lacks the methylated cap structure of a typical eukaryotic mRNA.

Solution:

The presence of ribosome landing pad, IRES or internal ribosome entry site. This enables ribosome to bind without the requirement to recognize 5’ methylated structure of a typical cap.

The virus interferes with host cell cap recognition, in turn inhibiting cap-dependent translation of host proteins.

Problem:

Eukaryotic translation machine requires monocistronic mRNA, causing problem to make more than one protein type from single RNA.

Solution:

The viral mRNA acts as single mRNA transcript. The virus synthesizes several monocistronic RNA. A large polypeptide is synthesized from each RNA, which is later cleaved.

2. Example: - sense RNA viruses: Influenza virus (Orthomyxoviruses).

Problem:

The negative sense RNA is complementary to mRNA.

Solution:

The virus encode for an RNA dependent RNA polymerase in the eukaryotic host. This help in conversion of negative sense RNA to positive sense RNA, which then act similar to mRNA.