STANFORD UNIVERSITY MEDICAL CENTER 
STANFORD, CALIFORNIA 94305 
DEPARTMENT OF BIOCHEMISTRY 
PAUL BERG 
Willson Professor of Biochemistry 
December 17, 1979 
Dr. Donald Fredrickson, Director 
National Institutes of Health 
Building 1, Room 124 
Bethesda, Maryland 20014 
Dear Don, 
One of the principal recommendations in The Asilomar Conference Report 
on Recombinant DNA was that the guidelines for containment and administrative 
procedures governing recombinant DNA research should be reviewed continuously. 
We expected that with growing experience our views about the nature of the 
risks would change and this would be translated into corresponding changes 
in the detailed recommendations in the NIH Guidelines. It is to your credit 
that you prevailed in incorporating a procedure for orderly changes and this 
procedure, though time consuming, is working. 
I want to take this opportunity to comment on the proposed change 
governing cloning experiments in EL coli K-12 host-vector systems. When the 
group of which I was a member expressed our concern about potential risks 
associated with recombinant DNA research, we had in mind the possibility that 
such experimentation might employ a wide variety of EL coli strains and trans- 
missable vectors as host-vector systems. We imagined that some of these would 
be able to establish themselves in nature or in the intestinal tracts of man 
and animals. Had we known then that EL coli strain K-12 and non-transmissable 
plasmids or phages would be widely adopted as the preferred host-vector systems, 
and that this system would be as secure as current expert opinion and all the 
risk-assessment experiments have shown, I doubt that we would have raised the 
issue in the manner we did. I am persuaded by the evidence I have seen that 
molecular cloning of any DNA segments in EL coli K-12 using the array of 
present day cloning vectors is no longer of any real concern, certainly not 
enough to warrant the containment requirements or the bureaucratic, confusing 
and time consuming reporting procedures demanded by the present Guidelines. 
I believe that your recommendation to retain the requirement for con- 
tainment for virtually all cloning in EL coli K-12 and to modify the reporting 
procedures for such experiments is prudent, warranted and a step in the right 
direction. Moreover, I believe it would speed progress in this field without 
compromising the safety of the investigators, the public or the environment. 
With best personal regards. 
Sincerely 
PB:vs 
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