Was Re:... Hepadnaviruses??Related to retroviruses?

[Karl Fischer]

In article <3q6v22$qra at ixnews4.ix.netcom.com>, srussell at ix.netcom.com
(Sandra Russell) wrote:


> Excuse a lay question: since hepadnaviruses sort of look like 
> retroviruses, and have the same transmission patterns as HIV, and are 
> carcinogenic, and since their DNA replicase even has reverse 
> transcriptase activity, I wonder if they are related?  Is there any 
> homology at all to these viruses and the retroviruses?

When I first started working on hepadnaviruses, this was a fundamental
question asked by myself and other grad students in the lab. There was a
paper entitled "Close evolutionary relatedness of the hepatitis B virus
and murine leukemia virus polymerase gene sequences" by Roger Miller
(Virology 164 p147-155, 1988) which attempted to address this. Regions of
the hepatitis B polymerase do indeed share homology with retroviral
reverse transcriptases. As well, there is some homology between gag and
hepatitis core protein (Miller and Robinson, PNAS 83, 2531-2535, 1986).

 
> Could retroviruses be hepadnaviruses that just got packaged wrong (along 
> with some RT?)
 
Hmmm...good question, let us center on the differences. Hepadnaviruses use
protein priming (similar to adenoviruses and bacteriophages phi29 and
PRD1) to initiate first strand DNA synthesis while retroviruses use
tRNAs.The hepadnavirus replication involves a nuclear unintegrated species
(covalently-closed circular) ds DNA while retroviruses require integration
of ds DNA into the host DNA. Roughly speaking, retros have a genetic
complement which is >3X larger than hepadnaviruses, as well as more gene
products/regulatory elements.

To your original question, based on the above perhaps hepadnaviruses are
streamlined decendants of retroviruses instead of the reverse? Thoughts
anyone?

Cheers

Karl

-- 
Karl Fischer
kfischer at gpu.srv.ualberta.ca
tyr-2 at bones.biochem.ualberta.ca