Fidelity of DNA Polymerase δ Holoenzyme from Saccharomyces cerevisiae:  The Sliding Clamp Proliferating Cell Nuclear Antigen Decreases Its Fidelity

DNA polymerases δ and ε (pol δ and ε) are the two major replicative polymerases in the budding yeast Saccharomyces cerevisiae. The fidelity of pol δ is influenced by its 3‘−5‘ proofreading exonuclease activity, which corrects misinsertion errors, and by enzyme cofactors. PCNA is a pol δ cofactor, called the sliding clamp, which increases the processivity of pol δ holoenzyme. This study measures the fidelity of 3‘−5‘ exonuclease-proficient and -deficient pol δ holoenzyme using a synthetic 30mer primer/100mer template in the presence and absence of PCNA. Although PCNA increases pol δ processivity, the presence of PCNA decreased pol δ fidelity 2−7-fold. In particular, wild-type pol δ demonstrated the following nucleotide substitution efficiencies for mismatches in the absence of PCNA: G·G, 0.728 × 10-4; T·G, 1.82 × 10-4; A·G,