Involved in DNA damage recognition. Binds DNA containing O(6)-methylguanine and larger O(6)-alkylguanine adducts. The DNA is bent, the damaged base is rotated out of the DNA duplex into a hydrophobic binding pocket (nucleotide flipping), with Arg-39 donating a hydrogen bond to the orphaned cytosine to stabilize the extrahelical DNA conformation. This structural change in DNA presents the lesion to the nucleotide excision repair (NER) pathway (PubMed:16679453, PubMed:19516334, PubMed:23112169). The affinity for O(6)-alkylguanine adducts increases with the size of the alkyl group. Low affinity small O(6)-alkylguanines are directed to the global genome repair pathway of NER via rhp7-rhp16 and rhp41-rhp23, while strong binding to bulky O(6)-alkylguanines stalls the transcription machinery and diverts the damage to the transcription-coupled repair pathway of NER via rhp26 (PubMed:22658721). 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.