DNA polymerase λ promotes error-free replication through Watson–Crick impairing N1-methyl-deoxyadenosine adduct in conjunction with DNA polymerase ζ

In a previous study, we showed that replication through the N1-methyl-deoxyadenosine (1-MeA) adduct in human cells is mediated via three different Pol tau/Pol theta, Pol zeta, and Pol.-dependent pathways. Based on biochemical studies with these Pols, in the Pol tau/Pol theta pathway, we inferred a role for Pol theta in the insertion of a nucleotide (nt) opposite 1-MeA and of Pol theta in extension of synthesis from the inserted nt; in the Pol eta pathway, we inferred that this Pol alone would replicate through 1-MeA; in the Pol zeta pathway, however, the Pol required for inserting an nt opposite 1-MeA had remained unidentified. In this study, we provide biochemical and genetic evidence for a role for Pol lambda in inserting the correct nt T opposite 1-MeA, from which Pol zeta would extend synthesis. The high proficiency of purified Pol lambda for inserting a T opposite 1-MeA implicates a role for Pol lambda-which normally uses W-C base pairing for DNA synthesis-in accommodating 1-MeA in a syn confirmation and forming a Hoogsteen base pair with T. The potential of Pol. to replicate through DNA lesions by Hoogsteen base pairing adds another novel aspect to Pol lambda's role in translesion synthesis in addition to its role as a scaffolding component of Pol zeta. We discuss how the action mechanisms of Pol lambda and Pol lambda could be restrained to inserting a T opposite 1-MeA and extending synthesis thereafter, respectively.