58 
unless the source of foreign DNA is pathogenic, or produces products 
dangerous to plants; then P3 is required. 
Slide 20 
Experiments with Plant 'Host- Vector' 
Systems 2. 
Physical 
Source of 'foreign' DNA Containment 
Species in which vector can replicate P2 
if harmful products possible P3 
Other species 
Foreign DNA purified (99%), and 
no harmful genes P2 
Foreign DNA not purified, and 
no harmful genes P3 
Foreign DNA contains 
harmful genes P4 
If the foreign DNA is derived from a species in which the vector is not 
known to replicate, that is, all other species, and thus the vector is in a 
sense also a foreign DNA, then more stringent requirements govern, and they 
vary from P2 to P4 depending on whether the DNA is purified and whether it 
contains harmful genes. Special, somewhat more stringent requirements are 
recommended for experiments with whole plants, and also the guidelines 
describe specific modifications of the physical containment specif icications 
in order to make them applicable to work with plants. 
May I have the lights, please? 
Theoretically there are a variety of organisms, both prokaryotes and 
lower eukaryotes — that is, fungi and yeast — which will be interesting and 
useful hosts for experiments with recombinant DNAs. Some may offer the 
special advantage of not infecting humans or important animals, or important 
ecological niches. However, a variety of technical developments are needed 
before useful vectors are available for these systems. The growth charac- 
teristics of such hosts indicate that the containment problems will be like 
those for coli K12 host-vector systems. The guidelines urge the develop- 
ment of these systems, and point out that the detailed recommendations made 
for _E_j_ coli K12 systems can be used as a guide in determining biological 
and physical containment requirements for these systems when that is 
required. 
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