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RYBICKI, ED ED at molbiol.uct.ac.za
Mon Oct 3 13:47:53 EST 1994

> Can anyone explain to me the selective or evolutionary advantage 
> negative strand RNA viruses?

On the face of it, there are very few perceived advantages for 
several of the strategies adopted by RNA viruses for their 
replication: (+)-sense ssRNA genomes are obviously (?) advantaged in 
that they can act as mRNA the moment they get into cells, so how 
have dsRNA viruses and (-)-sense ssRNA viruses - which both require 
a polymerase taken into cells with the genome - survived?  How 
have retroviruses and pararetroviruses - which both have an 
unnecessarily complicated replication strategy - made it into the 
present?  For that matter, what is the advantage of having a 
multi-component genome over having a single component?  Answer is: 
if evolution depended on simple logic, men definitely wouldn't have 
external genitals, and retroviruses probably wouldn't.  Replication 
strategies evolve because that is what WORKED at a given moment in 
evolutionary history, and has continued being refined so as to work 
better, without regard to the logic or the aesthetics of the 
situation.  Think on this: it may be possible to convert a (+)-sense 
RNA virus to a (-)-sense by simply biasing the relative amounts of 
the different strands being made (perhaps by swapping ori sequences 
on the diff strands?) - and maybe that is what happened.  That, or a 
dsRNA virus forgot to make a second strand....

 | 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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