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Slide 18 
Guidelines for use of Polyoma and SV40 as Vectors 
I. Vector must be a defective genome 
Finally, the helper could be a complete, intact virus. Any one of 
these alternatives allows the production of the defective viral particles, 
or of the defective containing a recombined foreign DNA; but the defective 
particles produced would, should they escape, have limited ability to infect 
susceptible species in a significant manner. 
In certain kinds of experiments no production of viral particles is 
required, and no helper may be needed. Biological containment is inherently 
greater in the absence of viral particles, since, as pointed out before, the 
cells themselves are relatively easy to contain. 
Keeping in mind these aspects of biological containment, we can look at 
the recommendations for physical containment with these experiments, and 
they are summarized on the next slide (19). 
The particular P-level depends on the source of the foreign DNA, on 
whether a defective polyoma or a defective SV40 (Simian Virus 40) is the 
chosen vector, and finally on whether or not virus particles are produced. 
Looking first at the experiments with defective polyoma vectors, under 
conditions where viral particles are produced, if the foreign DNA is itself 
from a non-pathogenic agent, P3 conditions are required, even if the DNA 
fragment was purified first and does not contain harmful genes. 
If the foreign DNA is from an organism with low pathogenicity, P4 must 
be used until such time as suitable tests indicate that only harmless genes 
are present. 
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