APPENDIX E 
possible sources of extrachromosoma I DNA are listed in Table 3 and the 
recommended combined containment given. For example, DNA from all or part 
of the genome of an animal virus requires P4 physical containment and 
an EK2 host vector system, or, alternatively, P3 and EK3. When the 
recombinants have been purified by cloning, and shown to be free of harmful 
regions of the viral genome, then experiments can be moved to P3 and EK2. 
When complementary DMAs, synthesized _i_n v itro from RNA preparations, are 
used in recombination experiments, the containment requirements are as 
described for isolated DNA preparat ions . Thus, for example, if the cDNA is less 
than 99 per cent pure, shotgun conditions are required. 
Guidelines for experiments with animal host-vector systems . Many recom- 
i b inant DNA experiments will involve the use of systems in which the host cells 
si! 
'j are eukaryote cells grown as single cells in tissue culture: useful vectors 
may include extrachromosoma I DNA elements such as organelle DNA, or the DNA 
: of viruses that infect the particular cells of interest. Given the current 
1 state of technology, viral DNAs are most I ikely to be used as vectors in the 
j near future. The cells themselves are fragile and fastidious and there is 
’ little or no chance that a living cell could escape from a laboratory in the 
i way that an E. col i cell might. Therefore containment considerations focus 
Ij on the viruses. Animal viruses can escape a laboratory in a viable form, 
ii especially if laboratory workers become infected. There are two animal viruses 
’i 
j whose DNAs are, now, technically useful as vectors; polyoma and simian virus 40 
I 
(SV40). The cleavage of these molecules with restriction endonucleases has been 
studied extensively. In their respective normal hosts, mouse for polyoma, rhesus 
I monkeys for SV40, neither virus causes a known disease. Polyoma does not infect 
1 
I 
I 
! 
I 
I 
Appendix E — 17 
