30 
in E^. col i K-12 hosts. They do not apply to other hosts where they 
may be able to replicate as a result of functions provided by the 
DNA inserted into the EK vectors. These are considered under other 
host-vector systems. 
(i ) Animal viruses 
P4 + EK2 or P3 + EK3 should be used to isolate DNA re- 
combinants that include all or part of the genome of an animal 
virus. This recommendation applies not only to experiments of the 
"shotgun" type but also to those involving partially characterized 
subgenomic segments of viral DNAs (for example, the genome of de- 
fective viruses, DNA fragments isolated after treatment of viral 
genomes with restriction enzymes , etc.). When cloned recombinants 
have been shown by suitable biochemical and biological tests to be 
free of harmful regions, they can be handled in P3 + EK2 conditions. 
In the case of DNA viruses, harmless regions include the late region 
of the genome; in the case of DNA copies of RNA viruses, they might 
include the genes coding for capsid proteins or envelope proteins. 
( i i ) Plant viruses 
. P3 + EK1 or P2 + EK2 conditions should be used to form DNA 
recombinants that include all or part of the genome of a plant virus. 
( i i i ) Eukaryotic organelle DNAs 
The containment conditions given below apply only when the 
organelle DNA has been purified. 6 Mitochondrial DNA from primates: 
6 
The DNA preparation is defined as purified if the desired DNA represents 
at least 99% (w/w) of the total DNA in the preparation, provided that it 
was verified by more than one procedure. 
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