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.

-Cheers!!
-Micky

-- 
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.

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