Structure and mechanism of B-family DNA polymerase zeta specialized for translesion DNA synthesis

DNA polymerase zeta (Pol zeta) belongs to the same B-family as high-fidelity replicative polymerases, yet is specialized for the extension reaction in translesion DNA synthesis (TLS). Despite its importance in TLS, the structure of Pol zeta is unknown. We present cryo-EM structures of theSaccharomycescerevisiaePol zeta holoenzyme in the act of DNA synthesis (3.1 angstrom) and without DNA (4.1 angstrom). Pol zeta displays a pentameric ring-like architecture, with catalytic Rev3, accessory Pol31, Pol32 and two Rev7 subunits forming an uninterrupted daisy chain of protein-protein interactions. We also uncover the features that impose high fidelity during the nucleotide-incorporation step and those that accommodate mismatches and lesions during the extension reaction. Collectively, we decrypt the molecular underpinnings of Pol zeta's role in TLS and provide a framework for new cancer therapeutics. Cryo-EM structures of free and DNA-bound pol zeta holoenzyme from budding yeast reveal how this DNA polymerase ensures fidelity and facilitates lesion bypass during translesion DNA synthesis.