Open AccessRelease of 7-methylguanine residues whose imidazole rings have been opened from damaged DNA by a DNA glycosylase from Escherichla coli
Author(s) -
Christopher J. Chetsanga,
Thomas Lindahl
Publication year - 1979
Publication title -
nucleic acids research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 9.008
H-Index - 537
eISSN - 1362-4954
pISSN - 0305-1048
DOI - 10.1093/nar/6.11.3673
Subject(s) - dna glycosylase , dna , biology , guanine , biochemistry , imidazole , uracil , hypoxanthine , pyrimidine , dna repair , purine , histidine , pyrimidine dimer , enzyme , nucleotide , gene
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.