O6-メチルグアニン-DNAメチルトランスフェラーゼ(英: O6-methylguanine DNA methyltransferase、略称: MGMT)またはO6-アルキルグアニン-DNAアルキルトランスフェラーゼ(英: O6-alkylguanine DNA alkyltransferase、略称: AGT、AGAT)は、ヒトではMGMT遺伝子にコードされるタンパク質である[5][6]。MGMTはゲノムの安定性に重要であり、自然発生する変異原性DNA損傷である6-O-メチルグアニン(英語版)をグアニンに戻し、DNA修復や転写時のミスマッチやエラーを防ぐ役割を果たす。マウスでは、Mgmt遺伝子の喪失によってアルキル化試薬曝露後の発がんリスクが増大する[7]。細菌には2つのアイソザイムが存在し、Ada(英語版)、Ogt(英語版)と呼ばれている。
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^“Increased susceptibility to chemotherapeutic alkylating agents of mice deficient in DNA repair methyltransferase”. Carcinogenesis21 (10): 1879–83. (October 2000). doi:10.1093/carcin/21.10.1879. PMID11023546.
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^“Loss of expression of DNA repair enzymes MGMT, hMLH1, and hMSH2 during tumor progression in gastric cancer”. Gastric Cancer6 (2): 86–95. (2003). doi:10.1007/s10120-003-0213-z. PMID12861399.