College of Physicians & Surgeons of Columbia University | New York, N. Y. 10032 
DEPARTMENT OF MICROBIOLOGY 701 West 168th Street 
October 16, 1979 
Dr. Donald Frednickson 
Director 
National Institutes of Health 
Bethesda, Maryland 20205 
Dear Donald: 
I write to express my support of the Recombinant DNA Advisory Committee ' s 
recent decision to exempt from the Guidelines recombinant DNA experiments 
in which the recombinant molecules are cloned in E. coli K-12 hosts not 
containing conjugation- proficient plasmids or generalized transducing 
phages and which employ as vector a nonconjugative plasmid, or lambda 
or lambdoid bacteriophage. The risk assessment data available, and 
the extensive safe use of K-12 in a large number of laboratories make 
the RAC's decision timely and sound. It seems unnecessary at this 
stage in our experience to repeat all the findings reported concerning 
the inability of K-12 to colonize efficiently. Moreover, recent un- 
published studies have given great strength to the safety of biological 
containment afforded by nonconjugative plasmids: no transfer of plasmid 
pBR322 occurred to other enteric bacteria, even from a wild-type K-12 
host after almost a week in the human intestine. 
I had the opportunity to discuss this matter with a number of infectious 
disease experts at the recent meeting of the Infectious Diseases Society. 
These were persons who had had particular experience with enteric 
pathogens, and were also very knowledgeable about plasmid biology. 
All favored the change in guidelines on the basis of their belief that 
these recombinant ENA molecules in EKL or EK2 host -vector systems do 
not constitute a biological hazard. 
My support of RAC's act ion is based on the judgement that the type of 
experiments under consideration do not constitute a hazard to the health 
of humans, other animals, or plants and that it becomes increasingly 
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