7,8-Dihydro-8-oxoguanine (8-oxoG) is an abundant and mutagenic DNA lesion. In Saccharomyces cerevisiae, the 8-oxoG DNA N-glycosylase (Ogg1) acts as the primary defense against 8-oxoG. Here, we present evidence for cooperation between Rad18-Rad6-dependent monoubiquitylation of PCNA at K164, the damage-tolerant DNA polymerase eta and the mismatch repair system (MMR) to prevent 8-oxoG-induced mutagenesis. Preventing PCNA modification at lysine 164 (pol30-K164R) results in a dramatic increase in GC to TA mutations due to endogenous 8-oxoG in Ogg1-deficient cells. In contrast, deletion of RAD5 or SIZ1 has little effect implying that the modification of PCNA relevant for preventing 8-oxoG-induced mutagenesis is monoubiquitin as opposed to polyubiquitin or SUMO. We also report that the ubiquitin-binding domain (UBZ) of Pol eta is essential to prevent 8-oxoG-induced mutagenesis but only in conjunction with a functional PCNA-binding domain (PIP). We propose that PCNA is ubiquitylated during the repair synthesis reaction after the MMR-dependent excision of adenine incorporated opposite to 8-oxoG. Monoubiquitylation of PCNA would favor the recruitment of Pol eta thereby allowing error-free incorporation of dCMP opposite to 8-oxoG. This study suggests that Pol eta and the post-replication repair (PRR) machinery can also prevent mutagenesis at DNA lesions that do not stall replication forks.
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