title: Release of 7-methylguanine residues whose imidazole rings have been opened from damaged DNA by a DNA glycosylase from Escherichia coli.
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 DNA with dimethyl sulfate followed by prolonged incubation at pH 11.4. These substituted formamidopyrimidine residues are actively removed from DNA by a DNA glycosylase present in E. coli cell extracts. The enz;me shows no apparent cofactor requirement and has a molecular weight of about 30 000. The release of ring-opened 7-methyl-guanine residues is due to a previously unrecognized activity, different from the three known E. coli DNA glycosylases that release uracil, 3-methyladenine, and hypoxanthine from DNA. This enzyme may serve to repair a major secondary alkylation product in DNA. In addition, it may remove nonmethylated purines, whose imidazole rings have been opened, from X-irradiated DNA.
mesh_terms: D004247:DNA / Q000528:radiation effects*; D004260:DNA Repair; D004926:Escherichia coli / Q000201:enzymology*; D006026:Glycoside Hydrolases / Q000378:metabolism*; D006147:Guanine / Q000031:analogs & derivatives* / Q000032:analysis; D007093:Imidazoles; D008970:Molecular Weight
chemical_list: D007093:Imidazoles; D006147:Guanine; D004247:DNA; D006026:Glycoside Hydrolases