Involved in DNA damage recognition. Binds DNA containing O(6)-methylguanine and larger O(6)-alkylguanine adducts, and to double-stranded DNA that contains an AP (apurinic/apyrimidinic) site (PubMed:16027108, PubMed:18084297, PubMed:19269902, PubMed:20921378). Binds to the damaged base and flips the base out of the DNA duplex into an extrahelical conformation, which allows processing by repair proteins (PubMed:18084297). Works in partnership with the nucleotide excision repair (NER) pathway to enhance the repair of the O(6)-alkylguanine adducts larger than the methyl adduct (PubMed:19269902, PubMed:20921378). Also prevents methyl-directed mismatch repair (MMR)-mediated attack of the O(6)-alkylguanine:T mispairs for the larger alkyl groups (PubMed:20921378). Interacts with HelD and UvrA. Does not have alkyltransferase activity. A tryptophan residue replaces the cysteine at the known active site of MGMT. Belongs to the MGMT family. ATL subfamily.