Viruses and Evolution

RYBICKI, ED ED at molbiol.uct.ac.za
Mon Jul 25 02:53:56 EST 1994


> From:          fostercmd at aol.com (FOSTERCMD)
> Subject:       Viruses and Evolution
> Date:          25 Jul 1994 02:33:03 -0400

> This post is designed to provide a forum on ideas/theories and 
questions
> related to the origin of viruses and their role in evolution.
> 
> What evolved first; bacteriophage T7 or E. Coli ?

Chickens and eggs...T7 is a coliphage; one has to assume the host 
evolved before the parasite, n'est-ce pas?

> Why is the ocean the richest and most diverse source of viruses?

Becase the ocean is also the richest source of bacterial (and maybe 
other type) diversity...an experiment done a couple of years ago 
showed that we have identified only 10% or less of the genera, let 
alone species, of bacteria present in sea water (they PCRed up 
ribosomal DNA, cloned, and sequenced the library).  Where you have a 
rich diversity of life, so also will you have a rich diversity of 
viruses.

> Is there any sequence connection between the four major types of 
viruses
> (i.e ds, ss, RNA and DNA)?

 Again, you need to look at Eugene Koonin's article in CRC Critical 
Reviews (sorry, no ref offhand - I had a preprint): in it he 
discusses the likely evolutionary pathway followed by a big chunk of 
(presently known) viruses.  Makes quite persuasive arguments for 
most of the RNA viruses we know of (except phages) having common 
origins, as cassettes of polymerase and associated genes which have 
accreted others by recombination over the geological ages since 
their origin.  There are arguments for linking ss and ds RNA 
viruses, and plus- and minus-sense genome viruses, in terms of 
evolutionary history (eg: a dsRNA virus of fungi has some sequence 
homology with an ssRNA virus of plants; plus- and minus-strand RNA 
genome viruses can be shown to have some homology between their 
replicases).  But don't go looking for a common thread linking all 
viruses: most phages are VERY different to most other viruses; DNA 
and RNA viruses probably don't have a common origin, and DNA viruses 
probably have several origins.

  _________________________________________________________________
 | Ed Rybicki, PhD          |         Well, I tip my hat           |
 | (ed at micro.uct.ac.za)     |      To the new constitution         |
 | Dept Microbiology        | Take a bow for the new revolution... |
 | University of Cape Town  |  Then I get on my knees and pray     |
 | Private Bag, Rondebosch  |   We don't get get fooled again...   |
 | 7700, South Africa       |                                      |
 | fax: xx27-21-650 4023    |      - Pete Townshend, 1972          |
 | tel: xx27-21-650 3265    |      (Won't get fooled again)        |
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