APPENDIX E 
unavailable. 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 virus particles since, as pointed 
out before, cells themselves are relatively easy to contain. 
With these aspects of biological containment in mind, the guidel ines 
specify required physical containment for these experiments, as summarized 
in Table 4. The particular levels of physical containment depend on the 
source of the foreign DNA, whether defective polyoma or defective SV40 is 
the chosen vector, and finally on whether or not virus particles are produced. 
Considering first experiments with defective polyoma vectors, under 
conditions where viral particles are produced ... i f the foreign DNA is from 
a nonpathogen ic 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 and then experiments 
can be continued at the P3 level. Still considering polyoma vectors, P3 
conditions are required for experiments in which no virus particles are 
produced. When defective SV40 is the vector, and virus particles are produced, 
P4 conditions must be used and the foreign DNA must be from a nonpathogen ic 
organism. Experiments can be done in P3 only after extensive and specified 
kinds of purification of the DNA and demonstration that no genes for toxic products 
are present. SV40 can not be used at all for experiments with DNA from pathogenic 
organisms. When no SV40 virus particles are produced, experiments with recombinant 
derived from nonpathogen ic agents can be carried out in P3 conditions. 
Appendix E — 19 
