Hadden C T, Foote R S, Mitra S
J Bacteriol. 1983 Feb;153(2):756-62. doi: 10.1128/jb.153.2.756-762.1983.
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.
枯草芽孢杆菌的细胞提取物含有一种甲基转移酶,该酶似乎能在原位从DNA中的O6-甲基鸟嘌呤上去除O6-甲基基团。如同在大肠杆菌中一样,此反应以化学计量方式进行。然而,该酶的基础水平(每个细胞约240个分子)在枯草芽孢杆菌中显著高于大肠杆菌。此外,与大肠杆菌一样,在用低浓度的N-甲基-N'-硝基-N-亚硝基胍(MNNG)进行适应性处理后,由于从头合成蛋白质,甲基转移酶水平会增加一个数量级。伴随着适应性变化,枯草芽孢杆菌细胞对挑战剂量的N-甲基-N'-硝基-N-亚硝基胍的杀伤和诱变作用变得更具抗性。我们提供证据支持以下假设:枯草芽孢杆菌中大多数由N-甲基-N'-硝基-N-亚硝基胍诱导的突变是鸟嘌呤到腺嘌呤的转换类型。