Release of 7-methylguanine residues whose imidazole rings have been opened from damaged DNA by a DNA glycosylase from Escherichla coli

摘要: Abstract Double-stranded DNA containing 7-methylguanine residues whose imidazole rings have been opened, i.e. 2,6-diamino-4-hydroxy-5-N-methylformamido-pyrimidine residues, may be prepared by treatment of with dimethyl sulfate followed prolonged incubation at pH 11.4. These substituted formamidopyrimidine are actively removed from a glycosylase present in E. coli cell extracts. The enz;me shows no apparent cofactor requirement and has molecular weight about 30 000. release ring-opened 7-methyl-guanine is due to previously unrecognized activity, different the three known glycosylases that uracil, 3-methyladenine, hypoxanthine DNA. This enzyme serve repair major secondary alkylation product In addition, it remove nonmethylated purines, X-irradiated