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Intravirion nucleic acid replication

Olav Hungnes ohungnes at bioslave.uio.no
Sun Aug 27 17:03:52 EST 1995

Karl Fischer (kfischer at gpu.srv.ualberta.ca) wrote:
: The virus we work with (hepatitis B virus) encapsidates a pregenomic RNA
: which is reverse transcribed WITHIN the virus capsid to give the partially
: double-stranded DNA genome.

: My question is - What other viruses demonstrate intravirion replication of
: their genome as opposed to ex virion synthesis then encapsidation?

: I suspect caulimovirus (another pararetrovirus) does this but am curious
: as to what other viruses utilize this strategy.

: Cheers

: Karl

It seems that some retroviruses perform partial reverse 
transcription in the virions (somebody in Gallo's group 
has been working on this, I think). I would guess that 
depletion of dNTPs is a limiting factor here, as particle
maturation happens more or less simultaneously with, or after,
virion budding. I wouldn't be surprised if the reverse 
transcription reaction of the incoming genome also happens
within a more or less complete nucleocapsid complex.

Maybe the crucial difference between hepadna- and retrovirus 
reverse transcription is that the hepadnaviruses assemble a structure 
with active polymerase and RNA genome at a stage when dNTPs from
the mother cell are still freely available, whereas the retroviruses
do not.

Do you think there is a connection between this and the funny way
hepadnaviruses primes their first-strand synthesis? This quite 
effectively males sure that nothing but virus RNA is used as template,
I would think. A prematurely activated retrovirus RT would perhaps
be too promiscuous. As far as I've understood, you can't assay
hepadnavirus RT activity using an exogenous template.

OTOH, the synthesis of the viral RNA genome, which is the real 
multiplication step, is catered for by the cellular RNA pol
2 and takes place outside any virus-generated structures in both 
hepadna- and retroviruses, I guess. 

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

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