Alkylbase DNA glycosidases []are DNA repair enzymes that hydrolyse the deoxyribose N-glycosidic bond to excise various alkylated bases from a damaged DNA polymer. In Escherichia coli there are two alkylbase DNA glycosidases: one (gene tag) which is constitutively expressed and which is specific for the removal of 3-methyladenine (), and one (gene alkA) which is induced during adaptation to alkylation and which can remove a variety of alkylation products (). Tag and alkA do not share any region of sequence similarity. In yeast there is an alkylbase DNA glycosidase (gene MAG1) [, ], which can remove 3-methyladenine or 7-methyladenine and which is structurally related to alkA. MAG and alkA are both proteins of about 300 amino acid residues. While the C- and N-terminal ends appear to be unrelated, there is a central region of about 130 residues which is well conserved.
