THE MUTAGENIC ACTION OF NITROUS ACID ON „SINGLE-STRANDED” (DENATURED) HEMOPHILUS TRANSFORMING DNA

Abstract

(1) New antibiotic resistance markers were not observed following nitrous acid treatment of native hemophilus DNA. This confirms the recent report of Stuy and is in contrast with the positive results of other transforming DNAs. (2) Similar treatment of denaturated hemophilus DNA followed by renaturation yielded large numbers of transformable resistance markers to five different antibiotics. (3) The resistance of the newly formed markers to continued exposure to nitrous acid is difficult to explain. A small fraction of natural markers is also less sensitive to this agent, so there is a precedent for such insensitivity. Possibly nitrous acid makes a mutagenic agent of DNA and the new markers are generated by this mutagenic DNA acting on the genome of the recipient cell by a nongenetic chemical interaction. (4) The common practice of correcting the mutation rate on the assumption that the new markers have the same sensitivity as the natural markers was found to be invalid for this system. (5) Experiments failed to account for the difference in response of native pneumococcal and hemophilus DNAs to nitrous acid.