14 . 
(iv) P ROKAR YOTIC PLASMID & PHAGE DMAs 
Pl asmid a nd__P ha g o Fr om H osts t hat Na tural ly Ex change Go nes 
with E. coli. 
DMA recombinants formed from plasmid genomes or phage genomes from 
phages known to propocjate in cells with known antibiotic resistance should 
only be studied under P3 containment. This also holds for experiments 
with recombinants from plasmid or phage genomes that have not been 
characterized with regard to pathogenic components. We consider P3 to be 
the minimal level of containment for any experiments not specifically 
mentioned here but of this category. Any experiments involving ■ recomb i nan 
DMA of known pathogenicity or from pathogenic strains also mandates P3 
containment. Experiments with known non-pathogens' plasmid and phage are 
P1-P2. 
PI as mi ds a nd P hage fro m Ho sts that do not N atural l y Ex change 
Genes w ith E. co l i. 
Because of the previously described inherently high degree of 
hazard using an EK host system, all DMA recombi nants formed wi th plasmids 
or phage containing resistance genes tc clinically significant antibiotics 
should be deferred. Since no adequate and acceptable definition for 1 hicr 
purified and characterized" segments of plasmids and phage genomes present 
exists, all work with such putati vely puri tied and characterized genome 
segments would wisely be done at P4 containment. Once it is demonstrated 
that such work is not potentially of high risk, these studies can then be 
dropped down to P3 containment. 
Note: cDNAs (i.e. complementary DMAs) synthesized Ir, vi tr o carry with them 
the analogous system of physical restraints. 
( d ) E XPER IMENTS W ITH OT HER PROKARYOT IC HOST -VECTORS 
The major thrust of our opinions on this section is presented 
earlier where we discuss the EK system and the essential problem of 
finding another and more suitable biological host system. Once this host- 
vector system is decided upon, fuTly studied, and then accepted, studies 
in other systems should be dropped from recombinant DNA analysis. Until 
this new host vector system is settled upon, all other non EK system sturii 
can be deferred. The exception to this, of course would be specific straw! 
being agreed upon as potential and safer replacements for the present EK 
system. And initially this work, depending on the studies being carried 
out, should be restricted to P3 or P4 containment. 
[ 365 ] 
