RNA Viruses

Virtually all known plant viruses contain RNA as the genetic material, instead of DNA. So, too, do several bacteriophages, some animal viruses (such as polio virus and influenza viruses), and the retroviruses, which are responsible for many tumors and for acquired immune deficiency syndrome (AIDS).

There are many schemes by which RNA viruses replicate their genetic material. In each case, however, RNA viruses must be able to convert RNA to DNA (like the retroviruses) or they must be able to replicate RNA using an RNA-dependent RNA polymerase.

RNA genomes can consist of single stranded RNAs, double stranded-RNAs, or even segmented RNAs (several separate RNA molecules). RNA-copying enzymes all lack proofreading abilities, so they are much more prone to errors than DNA polymerases. This enables these viruses to mutate and evolve far more rapidly than the organisms they infect, enabling such a virus to change so rapidly that it evades or counteracts the host's defense mechanisms.

See also: Retrovirus Replication

INTERNET LINKS:

> 1.All the Virology on the WWW

> 2. HIV Insite

> 3. General Replication Strategies for RNA Viruses