A Novel 3-Methyladenine DNA Glycosylase from Helicobacter pylori Defines a New Class within the Endonuclease III Family of Base Excision Repair Glycosylases

摘要: The cloning, purification, and characterization of MagIII, a 3-methyladenine DNA glycosylase fromHelicobacter pylori, is presented in this paper. Sequence analysis the genome pathogen failed to identify open reading frames potentially coding for proteins with activity. putative product HP602 frame, reported as an endonuclease III, shares extensive amino acid sequence homology some bacterial members family has canonic active site helix-hairpin-helix-GPD motif. Surprisingly, predicted H. pylori III encodes 25,220-Da protein able release 3-methyladenine, but not oxidized bases, from modified DNA. MagIII no abasic lyase activity displays substrate specificity 3-methyladenine-DNA type I Escherichia coli (Tag) because it recognize 7-methylguanine or hypoxanthine substrates. expression magIII frame null E. (tag alkA) restores mutant partial resistance alkylating agents. MagIII-deficient cells show alkylation-sensitive phenotype. wild exposed agents present adaptive response by inducing magIII. thus novel member family, which biochemical properties described any group until now.