MPG, a 3-methyladenine DNA glycosylase, removes the alkylated DNA base 3-methyladenine (Samson et al. 1991, Vickers et al. 1993, O'Connor 1993). MPG slides along DNA and scans for alkylated bases by inducing cooperative distortions of the double helix that expose nucleotides to the active site of the enzyme (Lau et al. 1998). MPG interacts with both alkylated and unmodified nucleotides and, at a low rate, cleaves unmodified bases (Berdal et al. 1998).