THE JOHNS HOPKINS UNIVERSITY 
SCHOOL OF MEDICINE 
DEPARTMENT OF MICROBIOLOGY 
725 N. WOLFE STREET 
BALTIMORE, MARYLAND 21205 
August 15, 1979 
Director 
Office of Recombinant DNA Activities 
Building 31, Roam 4A52 
National Institutes of Health 
Bethesda, MD 20205 
Dear Sir: 
I would like to express my support of the proposal of Rowe and 
Canpbell published in the Federal Register, 13 April, 1979, to exempt 
from the Recombinant DNA Regulations "recombinant DNA molecules that 
are propagated in E. coli K-12 hosts not containing conjugation- 
proficient plasmids or generalized transducing phages, when lambda or 
lambdoid bacteriophages or non-con jugative plasmids are used as vectors", 
excluding from such exemption presently prohibited experiments. In 
agreement with Rowe and Canpbell, I believe that we have had sufficient 
experience with E. coli K-12 host-vector systems to conclude that routine 
use of such systems does not require regulation to protect the safety of 
laboratory personnel or the public. In my opinion simple, standard 
microbiological practice is quite adequate for this purpose, as it is for 
demonstrably hazardous enteric pathogens. 
Sincerely 
Daniel Nathans, M.D. 
Professor and Director 
Department of Microbiology 
DN/lc 
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