Mailing Address: 
ZOOLOGY DEPARTMENT 
MORRILL SCIENCE CENTER 
Dr. Donald S. Fredrickson 
Director, NIH 
National Institutes of Health 
Bethesda, Maryland 20205 
Dear Dr. Fredrickson: 
The purpose of this letter is to urge against the approval of the proposed 
complete exemption of cloning in EL coli K-12 hosts from the NIH recombinant DNA 
guidelines and to encourage a more moderate relaxation of existing constraints as 
an alternate action. 
I doubt that my own view of the potential hazards of recombinant DNA cloning 
in EL coli K-12 hosts differs greatly from those advocating this exemption. Based 
on evolutionary considerations I consider it to be extremely unlikely that this 
laboratory strain of bacterium could unintentionally be converted into a viable 
pest or pathogen by the insertion of segments of foreign DNA. Evidence obtained 
to date suggests that it is extremely unlikely that the nonconjugative plasmids 
and mutant phage used as cloning vectors with 15. coli K-12 hosts would transfer 
to other bacteria at significant rates. Our own theoretical studies of the 
population biology of mobilizable nonconjugative plasmids suggests that even if 
these plasmids could be transfered to "wild" bacteria, in the absence of direct 
selection favoring their carriage, these nonself transmissible plasmids could not 
become established and would not be maintained in these natural populations (see 
the enclosed preprint). In general, my own view of the contamination risk associated 
with the use of 15. coli K-12 vectors is even more optimistic than when I first wrote 
to you about this problem two years ago. Our formal studies of the population 
biology of temperate phage have not gone as far as those on plasmids. However, if 
potential hosts for the mutant phage cloning vectors are as rare as they seem to 
be, (among the 120 strains examined in some studies we are doing of genetic variation 
in natural populations of 15. coli , only one was sensitive to wild type Lambda) at 
least on intuitive grounds, I believe that the contamination risk associated with 
these vectors would be extremely low and possibly even lower than that of plasmid 
vectors. 
While my view of the pathogen-contamination risk associated with the use of 
EL coli K-12 host-vector systems may not be too different from those advocating 
complete exemption, I don't believe that present information about these risks 
are sufficient to warrent so radical a change in regulations. This is the case 
even when one considers the negative evidence for hazards (we have yet to lose even 
a postdoctoral fellow to recombinant DNA disease much less a major molecular biologist. 
Significant questions remain unanswered; for example: 1) Could the production of 
hormones and other mammalian proteins confer pathogenic properties on 15. coli K-12? 
2) What is the likelihood of transfer and establishment of plasmid vectors in 
natural populations of enteric bacteria when there is selection favoring genes 
they are carrying such as the antibiotic resistance markers? I also believe that 
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