APPENDIX E 
recipient host cel I containing the DNA fragment of i nterest will be one 
of the normal aims of any recombinant experiment. The guidelines state 
that when a clone has been obtained from a shotgun experiment, and has 
been rigorously characterized, and when there is sufficient evidence that 
it is free of harmful genes, then experiments involving the clone can 
be carried out under P1 and EK1 conditions if the foreign DNA was from a 
species that exchanges genes with E. col i in nature, and under P2 and EK1 
conditions if it does not. 
Similarly, when the initial recombination involves a purified segment 
of the foreign chromosomal DNA, rather than a mixture, the potential for 
growth of a hazardous organism will be less, since the number of clones 
that must be examined to obtain the desired clone is markedly reduced. The 
guidelines define purified (or enriched) as meaning that the desired segment 
represents at least 99$ of the total DNA in the preparation, by weight, and 
further, they require evidence that no harmful genes are present. Under such 
circumstances the investigator may lower the containment conditions from these 
recommended for shotgun experiments with DNA of the same source, either by one 
step in physical containment or one step in biological containment, thus, 
for example, shotgun experiments with DNA from birds require P3 and EK2. A DNA 
fragment from birds that is free from harmful genes, and purified to 99$ purity 
prior to joining to a vector, would require either P2 and EK2 or P3 and EK1 . 
The final group of experiments utilizing E. col i host-vector systems 
that are considered are those in which the foreign DNA is itself from an 
extrachromosoma I element. As indicated in Figure 2 it is assumed that such 
DNA is purified away from chromosomal DNA prior to recombination. Various 
Appendix E — 16 
