28 
Prokaryotes that do not exchange genetic ir,fcr-£tio r 
E. coli - The minimum containment conditions for this class 
consist of P2 physical containment + an EK1 host-vector, and apply 
when the risk that the recombinant DNAs will increase the catho- 
genicity or ecological potential of the host is judged to be "iniral . 
Experiments with DNAs from pathogenic species (Class 2 '-ef . 5 plus 
plant pathogens) should use P3 + EK2. 
Experiments extending the range of resistance to therapeutical! y 
useful drugs and disinfectants should use D 2 + EK2 corta-i r re r t or richer 
depending on the virulence of the donor. 
( i i i ) Characterized clones of CNA ^ecorbi r ~a r ts de^.sp 
shotgun excerime r ts 
When a cloned DNA recombinant has been rigorous 1 ./ characterized" 
|b 
and there is sufficient evidence that it is free of harmful genes, 
then experiments involving this recombinant DNA can pe carried cut 
under PI + EK1 conditions if the inserted DNA is from a species that 
exchanges genes with E_. col i , and under P2 + EK1 conditions if not. 
The terms "characterized" and "free of harmful genes" are unavoidably 
vague. But, in this instance, before containment conditions lever than 
the ones used to clone the DNA can be adopted, the investigator must obtain 
approval from the granting agency. Such approval would be contingent upon 
data concerning: (a) the absence of potentially harmful genes e.g., 
sequences contained in indigenous turner viruses or which code for resit 
substances) , (b) the relation between the recovered and desired segment 
(e.g., hybridization and restriction endonuclease fragmentation analysis 
where applicable) , and (c) maintenance of the biological properties of 
the vector . 
[ 99 ] 
