RNA VIRUS REPLICATION - GENERAL
STRATEGIES
RNA viruses that do not have a DNA phase
Viruses that replicate via RNA intermediates need an RNA-dependent RNA-polymerase to replicate their RNA, but animal cells do not seem to possess a suitable enzyme. Therefore, this type of animal RNA virus needs to code for an RNA-dependent RNA polymerase.
No viral proteins can be made until viral messenger RNA is available; thus, the nature of the RNA in the virion affects the strategy of the virus:
Plus-stranded RNA viruses
In these viruses, the virion (genomic) RNA is the same sense as mRNA and so functions as mRNA. This mRNA can be translated immediately upon infection of the host cell
Examples:
poliovirus (picornavirus)
togaviruses
flaviviruses
Negative-stranded RNA viruses
The virion RNA is negative sense (complementary to mRNA) and must therefore be copied into the complementary plus-sense mRNA before proteins can be made. Thus, besides needing to code for an RNA-dependent RNA-polymerase, these viruses also need to package it in the virion so that they can make mRNAs upon infecting the cell.
Examples:
influenza virus (orthomyxovirus)