biosynthetic pathways can be pharmacologically active ainino acid 
derivatives. In the case of the Drosophila Vermillion locus and 
tryptophan pyrollase, the hazard might be small, but in other instances, 
less is known. For every single possibility like this one can think of, 
there may be 10 or 100 that one can not come up with, ahead of time. 
Because of the potential dangers and the leakiness of the biological 
containment, we feel that such work should be limited to P4 containment. 
Hi gher Pl ants - the combination of the airborne spread of E. 
- col i plus the knowledge that plants produce from 
bacterial metabolites alkaloids, other toxic compounds, and carry pathogenic 
agents strongly indicate that all work with 'higher plants' be done under 
P4 containment. 
( i i ) PROKARYOTIC DNA R ECOMB INANT S 
Prokaryotes _t hat_ naturally e xch ion ge g enetic inf ormat i on _vn th 
E. c ol i . P1-P2 type containment seems reasonable if it can be demonstrated 
in advance that DNA to be 'shotgunned' from such organisms contains no 
pathogenic properties and that it codes for no known antibiotic resistance 
markers. Any organism of potentially pathogenic or pathogenic property 
would call for P3 level containment. 
Prokar yotes that do not ordinarily e x c ha ncie_q ene ti c jjnJNarma ti o_n 
wi th E, col i - where it can be demonstrated that there is no potential 
for pathogenic or drug resistance transfer we would still call for P3 level 
containment due to the unknown hazard built into such experiments. P4 
containment should be mandatory for any experiments where the above hazards, 
though minimal in effect, are known. We strongly suggest deferring all 
such experiments where strong pathogenicity (e.g. cholera) in the prokaryote 
has been shown to exist. 
(iii) CHARACTERIZED CLONES OF DNA RECOMBINANTS DERIVED FROM SHOTGUN 
EXPERIMENTS 
In the case of cloned DNA which has been purified, shown not 
to contai n harmful genes , and is derived from an organism naturally 
exchanging DNA with IE. col i , we feel that P1-P2 type containment is 
sufficient. When this is to be done with DNA from an organism which 
normally does not exchange DNA with E. col i , we strongly suggest P3 level 
containment simply because of the 'built-in' unknown factors in such work. 
(b) PURIFIED CELLULAR DNA'S OTHER THAN PLASMIDS, BACTERIOPHAGES, AND OTHER 
VIRUSES 
"The formation of DNA recombinants from cellular DNAs that have been 
highly purified by physical and chemical techniques (i.e. not by cloning) 
and for which there is sufficient evidence that they do not contain harmful 
genes can be carried out under lower containment condition"? then used for 
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