title: A switch between DNA polymerases δ and λ promotes error-free bypass of 8-oxo-G lesions.
abstract: 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 δ 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 δ at 8-oxo-G after incorporation of correct C. This stalling at C:8-oxo-G can be overcome by a switch from pol δ to pols λ, β, or η, all of which are able to assist pol δ in 8-oxo-G bypass by translesion synthesis (TLS). Importantly, however, only pol λ selectively catalyzes the correct TLS past 8-oxo-G, whereas pols β and η show no selectivity and even preferentially enhance incorrect TLS. The selectivity of pol λ to promote the correct bypass depends on its N-terminal domain. Furthermore, pol λ(-/-) mouse embryonic fibroblast extracts display reduced 8-oxo-G TLS. 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 λ. 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 δ and λ.
authors.affiliation: Institute of Veterinary Biochemistry and Molecular Biology,  University of Zürich-Irchel, 8057 Zurich,  Switzerland.
authors.forename: Enni
authors.initials: E
authors.lastname: Markkanen
authors.forename: Benoît
authors.initials: B
authors.lastname: Castrec
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Villani
authors.forename: Ulrich
authors.initials: U
authors.lastname: Hübscher
mesh_terms: D000818:Animals; D001483:Base Sequence; D002478:Cells, Cultured; D004247:DNA / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004258:DNA Polymerase III / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D019951:DNA Polymerase beta / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D004260:DNA Repair / Q000502:physiology; D004261:DNA Replication / Q000502:physiology; D006147:Guanine / Q000031:analogs & derivatives* / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D034741:RNA, Small Interfering / Q000235:genetics
chemical_list: D034741:RNA, Small Interfering; C024829:8-hydroxyguanine; D006147:Guanine; D004247:DNA; C415367:DNA polymerase beta2; D004258:DNA Polymerase III; D019951:DNA Polymerase beta