Re infectivity of naked viral DNA

[Francisco Muril Zerbini]

On 18 May 1995, A. M. Lotto wrote:

> I was reading that caulimo viruses might be used to introduce desireable 
> genes into plants.  They are also said to be structurally and 
> functionally very similar to HBV.  I would assume then that caulimo 
> viruses like HBV form integrates with the host genome on occasion.

Sorry to disappoint you, but caulimovirus DNA does not integrate into the 
host genome.

> A couple of questions have occured to me.  First of all, is the mechanism 
> for the formation of this integrate known yet?  Second, the result of HBV 
> integration into the host human genes is hepatocellular cancer(or so it 
> is believed by the authors of this book, possibly in conjunction with a 
> carcinogenic co-factor), what is the result in plants?  

Like I said, the caulimovirus DNA is not integrated. Once the virus gets 
into the cell, the DNA is taken to the nucleus and transcribed. Two  
transcripts are produced: one slightly longer than full-length (35S) and 
one corresponding to gene VI (19S). These transcripts are translated and 
viral proteins are produced. The product of gene VI forms the matrix of 
virus-induced inclusion bodies in the cell cytoplasm. In these inclusion 
bodies the 35S RNA is reverse-transcribed by the product of gene V to 
generate new viral DNAs. New virions arise in the inclusion bodies (the 
CP is the product of gene IV).

What I think is the most interesting thing about caulimovirus replication 
is that the product of gene VI somehow allows the translation of 
downstream ORFs from the 35S RNA. There's many papers published on this.  

> If caulimovirus DNA is infectious on its own, does this also hold true 
> for HBV?  It is my understand there is a circular RNA (hepatitis 
> delta agent) associated with HBV that is compared with a 
> viroid.  Do caulimo viruses also contain this circular RNA?

There's no RNA associated with the viral particle, as far as I know. 

later,

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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