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Plant Viruses

Micky Krol mkrol at macc.wisc.edu
Thu Jan 19 14:34:12 EST 1995

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?
I just reviewed my boss's file on HepD, and consulted Field's Virology. 
With the discliamer that this is not a comprhensive nor up-to-date (the
most recent relevant paper i've got in hand is from 1992), i saw no
reference to any such related virus.
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.

All in all, a fascinating little beastie but unlikely to be a recent,
direct descendant of a plant viroid.  

I hope this clarifies matters.


Yup, these opinions are only my own, and sometimes not even that.  So
please don't blame them on anyone else, not even my Mom.

PGP public key available on request...I prefer to recieve letters that are
in envelopes over those on postcards

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