On Thu, 19 Jan 1995, Micky Krol wrote:
> In article <3flve5$crp at mserv1.dl.ac.uk>, <n.panjwani at ic.ac.uk> wrote:
>> > Now, as I remember, Hepatitis D Virus (HDV), which can only coinfect or
> > superinfect together with HepBV, is some 90% similar to a Tomato Virus, but
> > has no homology to any animal virus, let alone human virus. Could this
> > freaky virus have jumped out of a rotten tomato?
> > Naveed Panjwani
> > University of London.
>> What tomato virus would that be?
> Rather, HepD seems related to plant viroids and type I introns, by
> sequence comparison. HepD has a single stranded, circular RNA genome, and
> encodes the Delta antigen, which acts as a coat protein for the genome. I
> recall (but i may be wrong) that the antigen protein is dispensable for
> replication, thus like plant viroids relies on host enzymes to carry out
> its rolling circle replication w/ auto cleavage and ligation (that
> catalytic RNA stuff again!!). Thus the genome is about 4x the size of
> these plant viroids, and unlike the plant thingies encodes a protein. The
> regions of similarity (that is, those exclusive of the coding region) are
> reported to be about 60-70% similar between HepD and viroids.
Regarding the delta antigen, it is required for virus assembly.
As far as the phylogeny of HDV, I would refer you to Elena et al. 1991.
PNAS 88:5631-5634. Their theorysuggests that HDV is most closely related
to viroidlike satellit RNAs not necessarily viroids per se. Their
sequence analysis revealed HDV to be most closely related Subterranean
clover mottle virus. Regarding whether HDV jumped ship from plants to
animals, is fodder for intersting speculation.
Brick Ayola, Ph.D.
Tulane School of Medicine
***The problem with the gene pool is that there are no lifeguards***