Viruses and Evolution
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
> 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
> Is there any sequence connection between the four major types of
> (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.
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