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

AUTOR(ES)

Chetsanga, C J

RESUMO

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.

Documentos Relacionados

• Release of 7-methylguanine residues from alkylated DNA by extracts of Micrococcus luteus and Escherichia coli.
• Enzymatic excision from gamma-irradiated polydeoxyribonucleotides of adenine residues whose imidazole rings have been ruptured.
• 7-Methylguanine specific tRNA-methyltransferase from Escherichia coli.
• Ring-opened 7-methylguanine residues in DNA are a block to in vitro DNA synthesis.
• Enzymatic release of 7-methylguanine from methylated DNA by rodent liver extracts.