In article <567mua$4ih at net.bio.net>,
aiyar at ebv.oncology.wisc.edu (Ashok Aiyar) writes:
> It is more accurate to say that HBV replicates from DNA to DNA via
> an RNA intermediate (i.e DNA via RNA to DNA). Like HIV (and other
> retroviruses) this involves reverse transcription. The mechanisms
> evolved by HBV to generate a circular duplex DNA copy of the single
> plus strand genomic RNA is quite different than the mechanisms used
> by retroviruses to generate a DNA copy of their dimeric RNA genome.
Quite so, but the similarities are far more striking than the differences. The
hepadnaviruses (HBV family) have been called by some 'pararetroviruses'.
> Unlike retroviruses, HBV appears not to have evolved a specific
> mechanism to integrate it's DNA into the host.
True.
> In HBV associated
> hepatocellular carcinomas, the viral DNA is frequently found
> integrated into chromosomal DNA. The mechanism of this integration
> is unknown, but is likely to involve rolling circle replication, as
> there are usually multiple copies of the viral DNA juxtaposed in
> series in such integrations.
Not so. I am not aware of any evidence for rolling circle replication of HBV
DNA or of integration of greater-than-genome-length HBV DNA. Sites of
integration in the human genome seem to be random but there are hot-spots for
integration in the HBV genome (see, for example, Nagaya et al. (Gen. Develop.
1987; 1,773). These occur at the positions of the ends of the genomic DNA
strands, suggesting recombination by incoming virion DNA or the products of DNA
synthesis in the cytoplasm, some of which enter the nucleus to build up the pool
of ccc template DNA.
>> Curiously in some mammalian hepatitis B viruses (eg. woodchuck
> hepatitis virus) integrations at or near the N-myc2 locus are
> frequently observed in WHV associated hepatocellular carcinomas.
This is true, but may not be applicable to human HCC. Woodchucks have an extra
copy of n-myc (the pseudogene n-myc2), which is most often implicated, although
other myc genes also may be involved in some tumours. Association of HBV
integrations with human myc genes seem to be extremely rare, if they occur at
all. Furthermore, integrations of WHV DNA in the woodchuck genome seem to be
much more complex and rearranged than are HBV DNA integrations in the human
genome.
Tim
(who blames a truly gruesome EMACS editor for any typos and strange line
breaks.)
> [follow-ups redirected to bionet.vi
rology]
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