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Viruses vs plasmids

Francisco Muril Zerbini fmzerbini at UCDAVIS.EDU
Mon Jan 29 15:10:47 EST 1996

On 28 Jan 1996, Ed Rybicki wrote:

> Bruce Phillips:
> > 	Given recent comments, mine and Ed. Rybicki's. could there by any
> > objection to called viroids (or perhaps certain satellite RNAs) RNA plasmids.
> > The natural objection, as I see it, is that plasmids are defined as DNA
> > molecules.  But in all other attributes, viroids would seem to be the RNA
> > equivalent.
> They would, wouldn't they...except that they are potentially 
> pathogenic and offer no or no obvious survival advantage to their 
> hosts, which means they are much more similar to viruses in thast 
> respect.

I suppose a fundamental difference between plasmids and viroids is that
plasmids, as far as I know, always have at least one gene, encoding at
least one protein. Viroids do not encode any proteins. I'm not so familiar
with the hepatitis agent. But I agree that some plant satellite RNAs could
be considered similar to plasmids. 

| 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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