ROCHE INSTITUTE OF MOLECULAR BIOLOGY 
Nutley, New Jersey 07110 
December 11, 1979 
Dr. D. Frederickson 
National Institutes of Health 
Department of Health, Education 
and Welfare 
Public Health Service 
Bethesda, Maryland 20205 
Dear Dr. Frederickson: 
This short note is in regard to the revised guidelines 
on Recombinant DNA research of November 30, 1979. I am 
specifically referring to section III-O on page 69218, that 
deals with the downgrading of experiments using E. coli K12 
host vector systems. I am entirely in favor of this down- 
grading as written in the guidelines since all the scientific 
information that has accumulated over the past few years in- 
dicates that PI physical containment is sufficient when E. 
coli K12 is used. 
I hope that the NIH will accept this change as written. 
Sincerely yours, 
Herbert Weissbach, Ph.D. 
Associate Director and 
Chairman, Hoffmann-La Roche 
Recombinant DNA Biosafety 
Committee 
HW/kj 
