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While it is conceivable that a recombinant DNA molecule contain- 
ing the entire SV40 DNA plus a foreign DNA segment could infect 
humans and affect their health, this is extremely unlikely (26, 2 7, 28). 
The extensive knowledge of the genetics of SV40 virus shows clearly 
that it will not be possible to insert more than a very small piece 
of foreign DNA (less than a gene in size) into SV40 DNA without destroying 
its ability to form virus particles. The inserted piece will either replace 
essential genetic regions, destroy an essential gene by being inserted 
in the middle of it, or make the DNA molecule too big to be packaged 
into a virus particle. In addition to these intrinsic safety features, 
the Guidelines require that any recombinant DNA containing SV40 
sequences be so constructed that it cannot reproduce independently 
as a virus. Much of the work will be done with only short pieces of 
the SV40 DNA which do not have the capacity to make any virus at 
all. Otherwise stated, this type of work will not be done with SV40, 
but only with portions of DNA derived from it. In addition, stringent 
physical containment is required. 
d. Experiments involving the transfer of uncharacterized 
mixtures of IDNA segments derived From warmblooded 
animals into bacte ria 
Experiments of the type indicated in this title are believed to present 
a greater possible risk than others because they involve a conglomeration 
of undefined genes that might include DNA capable of causing disease. For 
this reason the Guidelines require more stringent containment when such 
mixtures of DNA segments are used. 
e. Use of oncogenic viruses 
It has been argued that the introduction into E. coli of the whole 
DNA or any purified segment of the DNA of any virus that is oncogenic 
(i.e., cancer-causing) in any species should not be permitted. The 
Guidelines do prohibit the use of DNA from viruses that could cause 
cancer in man, as well as certain other viruses causing cancer in 
animals (Section III-A-i). Those viral DNAs that may be used are 
subject to the most rigorous containment requirements (Section 
III-B-2 -c -i). 
