December 21, 1979 
Or. Donald S. Frederickaon 
Director 
National Inatitutea of Health 
Betheeda, Maryland 20205 
Dear Dr. Frederickaon: 
Aa biologiata working with recombinant DMA aoleculee, we atrongly aupport 
approval of the newly reviaed guidelinea on DMA recombinant reaearch aa 
publiahed in the Federal Bagiatar of Noveaber 30, 1979. 
We particularly aupport the recaanndation that all ezperiaenta uaing B coli K12 
aa hoat and non-con jugativa plaaaida or laabdoid bacteriophagea aa vectora be 
permitted under P1/BX1 containaant condi tiona. Our aupport for thia recoaaenda- 
tion ia baaed on the well-eatabliahed facta (1) that B coli B12 cannot colonize 
the hunan gaatrointeatinal ayataa and ar^not pathogenic for huaana even 
if ingeeted in vary large quantitiea (10 u cella), (2) that non-conjugative 
plaaaida are unable to actively tranafer their genetic information to other 
micro-organiama, and (3) that laabdoid phagea have a very reatricted hoat- 
range and are unatable in the gaatrointeatinal tract. Thua, the coabination 
of B. coli K12 with noo-conjugative plaaaida or laabdoid bacteriophagea 
conatitutea by itaelf a perfect natural barrier for propagation of recoabinant 
DMA material in huaana. 
Recoabinant DMA technology ia one of the moat potent toola of modern 
molecular biology and ia likaly to be eaaential for progreaa in atudying 
many of the fundamental biological prob laau which are challenging ua . 
The practice of theae techniques ahould be atrongly encouraged. 
limcerely, 
y I 1 Vl i I ml h ilfT 77}— 
LHt , *fC * 
l*CI 
la t, 
IS */} ,^<-1 
,*CI 
tici 
CAP, 
[ 589 ] 
