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There is one other word that is important to recognize, and that is the 
word "papovavirus . " Papovavirus — we virologists tend to have recombinant 
words — papovavirus means papilloma, polyoma, and vaculating virus, which is 
the old name for SV40. Two important viruses fall in this group — polyoma 
virus and SV40. They are very similar viruses. They are small, nonenveloped 
viruses, with a circular genome that is quite small, and they do have the 
ability to transform cells in tissue culture and produce tumors in certain 
laboratory rodents, not in higher animals. 
All right, now the question of using viral genomes or pieces of viral 
genomes in prokaryotic host-vector systems. We previously just put a lid on 
the whole thing. We said that until we know more, feel more comfortable 
with the system, let us just go very slow on these. We just said all viral 
genomes would have to be done at very high containment. Now we have had 
is much more discussion, and I think we have a much more rational classifica- 
tion of these viruses in relation to containment. I think although it is 
still an extremely tight, restrictive system, it is on a very rational basis. 
The justification is spelled out in footnote five of the Guidelines. 
We don't need to go to it now, but basically, for the whole virus genome, 
which carries any risk at all of producing infection, of moving out of the 
bacterium into the cells the way the polyoma experiment is postulated at 
least to look for, no change has been made for that scenario. That is, for 
DNA of a virus or reverse transcript, the DNA copy of a retrovirus, this 
has not been changed if the whole viral genome is present. 
But we feel that if one is working with just pieces of the viral genome, 
clearcut subviral, noninf ect ious segments of the genome, either the segmented 
portion from an RNA virus copied into DNA or a chopped up restriction enzyme 
fragment purified away from the rest of the viral genome, that this cannot 
infect, we know this, and it is consequently safer and can be worked with at 
one step of containment lower. 
However, we have maintained a great deal of caution in that if the seg- 
ment, free of the rest of the genome that is required for infect ivity, but 
if that segment has been incriminated in any way in cell transformation, if 
that is the crucial transforming gene or the gene that codes for some mem- 
brane protein that may turn a cell into malignant behavior, then that cannot 
be cloned at the lower containment level. That has to be treated as if it 
were the whole infectious genome as far as containment goes. That is a very 
restrictive point because we don't think that viral transformation is that 
simple an event. It is not just a matter of having a protein floating around 
in the environments of the cell. It is probably a very specific insertion of 
the DNA into the host cell at particular places, and the proteins changing 
regulation as they are produced within the cell. So that is a very cautious 
specification. 
Another criterion for setting containment is the nature of the host 
in which the virus naturally occurs — that is, whether it is a warm-blooded 
animal, a cold-blooded animal, or an invertebrate. Cold-blooded animals have 
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