Replication past O-6-methylguanine by yeast and human DNA polymerase eta

O-6-Methylguanine (m6G) is formed by the action of alkylating agents such a s N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) on DNA, m6G is a highly mutag enic and carcinogenic lesion, and it presents a block to synthesis by DNA p olymerases, Here, we provide genetic and biochemical evidence for the invol vement of yeast and human DNA polymerase eta (Pol eta) in the replicative b y-pass of m6G lesions in DNA, The formation of MNNG-induced mutations is al most abolished in the rad30 Delta pol32 Delta double mutant of yeast, which lacks the RAD30 gene that encodes Pol eta and the Pol32 subunit of DNA pol ymerase delta (Pol delta), Although Pol delta can function in the mutagenic bypass of m6G lesions, our biochemical studies indicate that Pol eta is mu ch more efficient in replicating through m6G than Pol delta, Both Poly and Pol delta insert a C or a T residue opposite from m6G; Pol delta, however, is more accurate, as it inserts a C about twice as frequently as Pol delta, Alkylating agents are used in the treatment of malignant tumors, including lymphomas, brain tumors, melanomas, and gastrointestinal carcinomas, and t he clinical effectiveness of these agents derives at least in part from the ir ability to form m6G in DNA, Inactivation of Pol eta could afford a usefu l strategy for enhancing the effectiveness of these agents in cancer chemot herapy.