Enhancement of deoxyribonucleic acid polymerase I-directed repair synthesis in toluene-treated Escherichia coli after growth in the presence of low levels of N-methyl-N'-nitro-N-nitrosoguanidine

Adaptive response of Bacillus subtilis to N-methyl-N'-nitro-N-nitrosoguanidine

Cell extracts of Bacillus subtilis contain a methyltransferase that appears to remove the O6-methyl group from O6-methylguanine in DNA in situ. This reaction proceeds in a stoichiometric fashion, as in Escherichia coli. However, the basal level of the enzyme (approximately 240 molecules per cell) is significantly higher in B. subtilis than in E. coli. In addition, the methyltransferase level increases by an order of magnitude as a result of de novo protein synthesis after adaptive treatment with a low concentration of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), as in E. coli. Concomitant with adaptation, B. subtilis cells become more resistant to both killing and mutagenesis by a challenge dose of N-methyl-N'-nitro-N-nitrosoguanidine. We present evidence to support the hypothesis that the majority of N-methyl-N'-nitro-N-nitrosoguanidine-induced mutations in B. subtilis are of the guanine-to-adenine transition type.

Genetic effects of N-methyl-N'-nitro-N-nitrosoguanidine and its homologs

Since the discovery of the mutagenic activity of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in 1960, this compound has become one of the most widely used chemical mutagens. The present paper gives a survey on the chemistry, metabolism, and mode of interaction of MNNG with DNA and proteins, and of the genotoxic effects of this agent on microorganisms, plants, and animals, including human cells cultured in vitro. Data on the carcinogenicity and teratogenicity of MNNG as well as on the genotoxic effects of homologs of MNNG are also presented.