Viral DNA insertion into host genome.

[Walter Ogston]

> In article <Pine.A32.3.91.950909123618.24020C-100000 at red.weeg.uiowa.edu>,
> volm timothy gerard <tvolm at blue.weeg.uiowa.edu> wrote:
> 
> > Hello,
> > 
> >          Was curious to know whether or not viral DNA intergration into 
> > the host genome was site specific, or sequence dependant. Was just 
> > thinking that this would make sense since non specific insertion into the 
> > host genome might prove fatal for the host. Anyone have any information 
> > on this?   Thanks, Tim Volm
> 
> I know that AAV integration into human chromosome 19 (I think) is site
> specific.  It is dependant on the terminal invered repeats which all
> parvoviruses have at both ends.  AAV is the only parvovirus known to
> integrate.
> 
> Don
> 
> Don Haut 
> Molecular Microbiology and Immunology
> University of Missouri-Columbia
> C601591 at showme.missouri.edu
> 314-882-3171
> 
I think that the present consensus on retrovirus integration is that it
happens all over the genome, but certain sequences are more likely to
get hit than others.  Different retroviruses show different degrees and
types of preference for target sequence.  

The situation is entirely different in phage; most temperate phage like
lambda have a specific integration (att) site in the host genome.  

There is an interesting evolutionary angle to this difference.  The
virus integrated into the genome of a single-celled organism is throwing
its lot in with the host.  There is strong selective pressure to choose
an integration site that does not disrupt any essential gene.  (This
isn't universal: mu takes its chances.)  The virus integrating in a cell
of a multicellular organism doesn't have quite the same constraints.
First the cell is (usually) diploid, and second the cell us normally not
on the germ line, and third in multicellular organisms there is an awful
lot of the genome that is not expressed in any one differentiated cell
type.  

How do we explain the difference between a retrovirus and AAV, then?
(homework problem). 
----------------------------------------------------------------------
Walter Ogston				ogston at hobbes.kzoo.edu
Department of Biology			Phone: (616)337-7010
Kalamazoo College			Fax:   (616)337-7251
Kalamazoo, MI 49006-3295