Strains of Escherichia coli K12 have been constructed as safer hosts for use in recombinant DNA research. These strains are unable to survive passage through the intestinal tracts of rats because of a constellation of mutations conferring bile sensitivity and requirements for diaminopimelic acid and thymine. Since death caused by diaminopimelic acid deprivation could release recombinant DNA before DNA is degraded because of thymine starvation, it is important to determine the "survival potential" of the released DNA's. Bacterial and plasmid DNA's extracted from bacterial cells are rapidly degraded when added to low dilutions of rat intestinal contents. This observation, coupled with the stringent requirements necessary for in vitro transformation or transfection, make in vivo transmission of naked recombinant DNA in the rat intestinal tract highly improbable.
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