In article <Cy5G7t.It5 at eecs.nwu.edu> markb at hook.eecs.nwu.edu (Mark E. Brodsky) writes:
>>>Thank you. Others have written me saying that retroviruses have two
>copies of their genome, such is the case with HIV for instance. Does
>anyone know why this is? I thought viruses were supposed to be models
>of efficiency. Aren't two copies of the same genome wasteful if the
>organism doesn't reproduce sexually?
"Models of efficiency"? I think not. In many viruses (at least all that
I have worked with) the output from an infected cell consists mostly of
noninfective particles - frequencies range from 10:1 for some HSV up to
1000's:1. These particles may be able to enter a cell and even to
initiate a round of replication, but are not able to complete infection to
form new particles. In many viruses, you can get DI (defective
interfering) particles, which actively inhibit replication of "real"
particles. Although there are many arguments as to the function of these
things, it seems plausible to me that there is no function. Viruses do
use their genome with tremendous efficiency (look at the number of
proteins an adenovirus genome can express) but they are too small to
build in clean regulatory functions. In many cases their best strategy
might be replicate like hell, and hope that their will be enough good
stuff in the output to keep going.
Of course, while this is a general statement, it doesn't address
the retrovirus two-genomes situation, which sounds more like a feature
than a bug. Could that be a redundancy to hopefully overcome possible
defects in one of the genomes?.
Ian York (york at mbcrr.harvard.edu)
Dana-Farber Cancer Institute, 44 Binney St., Boston MA 02115
Phone (617)-632-4328 Fax (617)-632-2627