title: O6-methylguanine mutation and repair is nonuniform. Selection for DNA most interactive with O6-methylguanine.
abstract: Mutations were induced in the ampicillinase gene of a bacteriophage f1/pBR322 chimera both by incorporation of O6-methyl-dGTP opposite T during DNA replication in vitro and by site-directed mutagenesis using O6-methylguanine-containing oligonucleotides. After passage of the DNA through Escherichia coli, analysis of 151 O6-methyl-dGTP-induced mutations indicated a significantly greater number of unmutated mutation sites than expected, whereas the mutated sites generally fit a Poisson distribution. The unmutated sites are assumed to be caused by the inability of some sequences to tolerate the presence of a tetrahedral methyl group within the confines of a Watson-Crick helix (Toorchen, D., and Topal, M.D. (1983) Carcinogenesis 4, 1591-1597). A consensus of the DNA sequences surrounding unmutated mutation sites was derived. The consensus sequence had significant similarity to the region of the rat Harvey ras oncogene containing the N-methyl-N-nitrosourea activated site for transformation (Zarbl, H., Sukumar, S., Arthur, A. V., Dionisio, M.-Z., and Barbacid, M. (1985) Nature 315, 382-385). We propose that direct alkylation at O6 of a guanine present within the consensus sequence may produce a DNA conformation less subject to repair. Mutation by O6-methylguanine-containing oligonucleotides demonstrated that repair of the O6-methylguanine lesions varied at least 3-4-fold with position of the lesion.
mesh_terms: D000478:Alkylation; D000667:Ampicillin / Q000378:metabolism; D001435:Bacteriophages / Q000235:genetics; D001483:Base Sequence; D002678:Chimera; D004247:DNA / Q000378:metabolism*; D004260:DNA Repair; D004926:Escherichia coli / Q000235:genetics; D006147:Guanine / Q000031:analogs & derivatives* / Q000378:metabolism; D009154:Mutation; D009857:Oncogenes; D010405:Penicillinase / Q000235:genetics
chemical_list: D006147:Guanine; D000667:Ampicillin; D004247:DNA; C008449:O-(6)-methylguanine; D010405:Penicillinase