Why negative strand RNA viruses?(was:none)

Olav Hungnes ohungnes at bioslave.uio.no
Tue Oct 4 04:27:28 EST 1994

RYBICKI, ED (ED at molbiol.uct.ac.za) wrote:
: > Can anyone explain to me the selective or evolutionary advantage 
: of
: > 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)        |

On the other hand, the ready-to use mRNA-sense genome of the plus strand 
virus comes on low amounts, perhaps only one per cell. One negative-sense 
genome, on the other hand, can in one transcription step give rise to 
many sense transcripts. 

Perhaps some insight can be sought in the arenaviruses whose genomic RNAs 
are ambisense, that is, at one end they are negative-sense and at the 
other end positive-sense. This seems to translate into regulation of early 
and late gene expression. And it is the negative-sense-encoded genes 
(polymerase and nucleocapsid protein) that are expressed first!

Olav Hungnes                 olav.hungnes at embnet.uio.no
National Institute               Phone  (+47)22042200
of Public Health                 FAX    (+47)22353605

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