Diploid Viruses?

[Olav Hungnes]

Ian A. York (york at mbcrr.dfci.harvard.edu) wrote:
: In article <Cy24L5.H9t at eecs.nwu.edu> markb at hook.eecs.nwu.edu (Mark E. Brodsky) writes:
: >Recently, I was browsing a Virology WWW page, when I came across a
: >referance to "Diploid" viruses. It seemed to imply that these were not
: >diploid in the usual sense of the word, but the server did not
: >elaborate any more on the subject. Could someone please explain what
: >is meant by a diploid virus? Thank you.

: I'm not sure if this is what was meant, but herpes simplex virus (and 
: most of the other herpes viruses) are pseduodiploid for some of their 
: genes.  This is because their genome contains repeated regions which 
: encode a couple of genes: (ascii herpes simplex virus: not to scale)  


:   ____                                   ________                 __
:  |____|---------------------------------|____|___|---------------|__|
:  ^^^^^^ b                             k ^^^^^^^^^^               ^^^^
:  gene a                                   a  ^^^^^               ^^^^
:                                                l   m           t   l 

: As this schematic is supposed to show, genes "a" and "l" are doploid, 
: while genes "b" to "k" and "m" to "t" are not.

: Hope this helps.

: Ian

Furthermore, the retrovirus particles contain two copies of the genomic
RNA. They will be "homozygous" if originating from a cell with only one 
provirus, and may be "heterozygous" when incorporating transcripts from 
two different proviruses (probably random) in a mixed infection setting. 
Recombination between the two copies seems to happen frequently.

Orthomyxovirus particles like influenza virus, which has its genome 
ditributed over nine RNA segments also seem to package more than nine RNA 
molecules, resulting in diploidy or oligoploidy for some genes, and 
perhaps omission of one or several genome segments in some particles. 
This is perhaps a rather slack mechanism to ensure that most particles 
contain a complete set.

I have the impression that there is great variation among the viruses in 
how stringently they package their genomes and exclude other genetic 
material.

Olav

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