APPENDIX H 
CERTIFICATION OF EK2 HOST -VECTOR SYSTEMS* * 
I. REPORT TO THE RECOMBINANT ADVISORY COMMITTEE 
FROM THE WORKING GROUP ON SAFER HOSTS AND VECTORS: 
LAMBDA PHAGE SYSTEMS 
Unanimously Accepted by the 
Recombinant Advisory Committee on 
January 15, 1977 
I. Standardized Laboratory Tests for EK2 Certification 
Based, in part, on the written suggestions of various members of 
the Working Group, four criteria were proposed to embody the essential 
requirements for certification. These criteria were approved unanimously 
by the Working Group to be recommended for adoption by the Advisory 
Committee in certification of X EK2 vector systems. 
A. Yield of Vector Phage 
The yield of vector phage (+ or - a model cloned fragment) 
10 
propagated under laboratory conditions should be no less than 10 /ml 
of unconcentrated crude lysate. 
B. The probability that a fragment cloned on the vector will form 
a persistent association with the permissive host used for its propagation 
and that this complex will then survive for 24 hours, outside the laboratory 

should be less than 10 This probability is calculated as the product 
of (1) and (2) below. 
(1) Number of fragment -containing surviving bacteria per 
output fragment -containing phage in the lysate. 
(2) Survival of bacteria after 24 hours under non-permissive 
test conditions as determined in a separate experiment 
carried out in the absence of phage. 
*A Workshop on Design of Tests for EK3 Host-Phage -Vector Systems 
was held at NIH July 19, 1977. A forthcoming report will be available 
from the NIH Office of Recombinant DNA Activities. 
Appendix H — 1 
