Mutation as an error in base pairing. I. The mutagenicity of base analogues and their incorporation into the DNA of Salmonella typhimurium.

Abstract

Reversion patterns of twenty-three mutants at two tryptophan loci (try C andD) inSalmonella typhimurium have been investigated after treatment with three specific mutagens. The compounds used were the base analogues, 5-bromouracil (BU) and 2-aminopurine (AP), and nitrous acid. The mutant alleles showed considerable specificity of response to the mutagens. The increased frequency of mutants after growth in the presence of base analogues was not due to selection of pre-existing mutants as shown by reconstruction experiments. It was determined that BU can be incorporated into the DNA of this organism by replacing thymine. A small amount of unaltered AP was recovered from the DNA of a purine-requiring mutant. These findings suggest that BU and AP induce “basepair transitons” inSalmonella typhimurium as had been previously observed for bacteriophage (Freese 1959).