A Switch Between Dna Polymerases Delta And Lambda Promotes Error-Free Bypass Of 8-Oxo-G Lesions

7,8-Dihydro-8-oxoguanine (8-oxo-G) is a highly abundant and mutagenic lesion. Replicative DNA polymerases (pols) are slowed down at 8-oxo-G and insert both correct cytosine (C) and incorrect adenine (A) opposite 8-oxo-G, but they preferentially extend A:8-oxo-G mispairs. Nevertheless, 8-oxo-G bypass is fairly accurate in vivo. Thus, the question how correct bypass of 8-oxo-G lesions is accomplished despite the poor extension of C:8-oxo-G base pairs by replicative pols remains unanswered. Here we show that replicative pol delta pauses in front of 8-oxo-G and displays difficulties extending from correct C:8-oxo-G in contrast to extension from incorrect A:8-oxo-G. This leads to stalling of pol delta at 8-oxo-G after incorporation of correct C. This stalling at C:8-oxo-G can be overcome by a switch from pol d to pols lambda, beta, or eta, all of which are able to assist pol delta in 8-oxo-G bypass by translesion synthesis (TLS). Importantly, however, only pol lambda selectively catalyzes the correct TLS past 8-oxo-G, whereas pols beta and eta show no selectivity and even preferentially enhance incorrect TLS. The selectivity of pol lambda to promote the correct bypass depends on its N-terminal domain. Furthermore, pol lambda(-/-) mouse embryonic fibroblast extracts display reduced 8-oxo-GTLS. Finally, the correct bypass of 8-oxo-G in gapped plasmids in mouse embryonic fibroblasts and HeLa cells is promoted in the presence of pol lambda. Our findings suggest that even though 8-oxo-G is not a blocking lesion per se, correct replication over 8-oxo-G is promoted by a pol switch between pols delta and lambda.