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

Abstract
Cell extracts of B. 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. The basal level of the enzyme (.apprx. 240 molecules/cell) is significantly higher in B. subtilis than in E. coli. 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 killing and mutagenesis by a challenge dose of N-methyl-N''-nitro-N-nitrosoguanidine. Evidence is presented 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.

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