Viruses as prey?

Francisco Muril Zerbini fmzerbini at UCDAVIS.EDU
Fri Sep 1 14:06:39 EST 1995


On 1 Sep 1995, Ian A. York wrote:

> I was thinking about the Hep delta virus which requires Hep B virus for 
> replication (HDV uses the HBV coat protein to surround its own nuvcleic 
> acids) - in the presence of HDV HBV titres go down (though not to zero, 
> and the liver damage is worse, so there's no therapeutic potential).  
> Adeno-associated virus is similar in that it requires adenovirus (or I 
> think a couple of other viruses) to replicate; I don't know for sure what 
> happens to adenovirus in the presence of AAV but I presume its 
> replication is impaired.  There are plant viroids that are similar 
>                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> although I've forgotten most of the tiny bit I knew about them.  
> 
> Perhaps these things are better described as "parasites" of the other 
> viruses rather than "predators", but the distinction is semantic, I think.

Viroids are completely autonomous entities. They do not need a helper
virus for replication and they do not have a coat protein (in fact their
ssRNA "genomes" do not encode any proteins). Some viroids cause very
serious diseases in plants (tomato, avocado, coconut trees) and therefore
are important pathogens/parasites/predators of plants, but not of other
viruses. 

There are, however, many examples of satellite viruses, which replicate
only when a helper virus is present, using either the helper virus coat
protein or its replication-associated enzymes. sTMV, sToRSV, sCMV
(cucumber mosaic virus, not cytomegalovirus...) are some that I can
remember right now, but there are many more. 

Murilo
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| Murilo Zerbini                   | Out of 3,000,000,000 DNA nucleotides, |
| Dep. of Plant Pathology          | human beings and chimpanzees have     |
| University of California, Davis  | 2,999,400,000 in common.              |
| fmzerbini at ucdavis.edu            |                                       | 
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