Phosphorylation of the p68 Subunit of Pol δ Acts as a Molecular Switch to Regulate Its Interaction with PCNA.

DNA polymerase delta (Pol δ) is a central enzyme for eukaryotic DNA replication and repair.Pol δ is a complex of four subunits p125, p68, p50 and p12.The functional properties of Pol δ are largely determined by its interaction with its DNA sliding clamp PCNA (proliferating cellular nuclear antigen).The regulatory mechanisms that govern the association of Pol δ with PCNA are largely unknown.In this study, we identified S458, located in the PCNA-interacting protein (PIP) motif of p68, as a phosphorylation site for PKA.Phosphomimetic mutation of S458 resulted in a decrease in p68 affinity for PCNA as well as the processivity of Pol δ upon encountering pause sites on a DNA template.Our results suggest a role of phosphorylation of the PIP motif of p68 as a molecular switch that dynamically regulates the functional properties of Pol δ.