Eukaryotic DNA polymerase δ (pol δ) is a member of the B family of polymerases and synthesizes most of the lagging strand during DNA replication. Yeast pol δ is a heterotrimer comprised of three subunits: the catalytic subunit (Pol3) and two accessory subunits (Pol31 and Pol32). Although pol δ is one of the major eukaryotic replicative polymerase, the mechanism by which it incorporates nucleotides is unknown. Here we report both steady state and pre-steady state kinetic studies of the fidelity of pol δ. We found that pol δ incorporates nucleotides with an error frequency of 10-4 to 10-5. Furthermore, we showed that for correct versus incorrect nucleotide incorporation, there are significant differences between both pre-steady state kinetic parameters (apparent K ddNTP and kpol). Somewhat surprisingly, we found that pol δ synthesizes DNA at a slow rate with a kpol of ∼1 s-1. We suggest that, unlike its prokaryotic counterparts, pol δ requires replication accessory factors like proliferating cell nuclear antigen to achieve rapid rates of nucleotide incorporation.
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