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.
HDV is dependent upon HBV because it needs the envelope glycoproteins, but
otherwise does not need any other HBV function for replication as shown by
studies of transfected in vitro synthesized RNA in uninfected, non-hepatic
cell lines. I think the homology you refer to is the structural homology
between genomes, the RNA genome of HDV being a closed, circular,
single-stranded RNA that can "collapse" into a mostly, rod-shaped RNA (I
don't know about Tomato Virus?). I believe that the structure of the viral
genome (in the case of HDV) has evolved from an RNA that could be copied
by cellular enzymes much in a manner similar to the X and Y RNAs that can
be 'replicated' by phage T7 DNA-dependent RNA-polymerase. Futher, that
this RNA has incorporated into it, a factor which may determine
specificity of replication, giving it an advantage over some other RNA
molecules which may also be copied, but may lack the ability to, for
example, copy the other polarity of RNA making it non-replicating. I doubt
that HDV was initially a plant virus gone amuck, I think HDV is the sole
virus in this particular class because we just lack the tools to easily
identify other similar viruses.
My opinions do not represent those of Rockefeller University, or at least
that's what I'm told.