45 
Slide 7 
EK2: high level of biological containment. 
Modification of existing E. coli 
K12 and plasmids and 
bacteriophage 
Modification by classical 
genetic techniques. 
Containment capability demonstrated 
by suitable laboratory tests. 
MODIFICATIONS TO YIELD A 'HOST-VECTOR' SYSTEM SUCH 
THAT FREQUENCY OF SURVIVAL OF THE 'FOREIGN' DNA 
FRAGMENT WILL BE 10 8 OR LESS, EXCEPT UNDER SPECIAL 
LABORATORY CONDITIONS 
(Responsibility for certification of putative E K2 systems lies with the 
NIH Recombinant DNA Program Advisory Committee) 
EK2 host-vector combinations afford a high level of biological contain- 
ment and are obtained by the modification of both E_^ coli K12 cells and 
relevant plasmids and bacteriophage. The modifications will be achieved by 
classical genetic techniques, and the level of containment must be demon- 
strated by suitable laboratory tests. 
More specifically, the guidelines state that the system of modified E. 
coli K12 hosts combined with modified vector must be such that the likeli- 
hood of escape and survival of the foreign DNA fragment in environments 
approximating natural environments will be one in 108 — that is, one in a 
hundred million or less. 
The recombinant is thus designed to survive and grow only under very 
fastidious laboratory conditions. While not stated in the guidelines, the 
NIH Recombinant DNA Molecule Program Advisory Committee has taken on the 
reponsibility for certifying putative EK2 systems. At this time none have 
been certified, although it is anticipated that several systems will be 
certified in the very near future. 
Various examples of the types of necessary modifications are suggested 
in the guidelines, specific modifications for both E. coli itself and for 
the vectors. 
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