Replication Protein A as a "Fidelity Clamp" for DNA Polymerase α

Abstract

The current view of DNA replication in eukaryotes predicts that DNA polymerase α (pol α)-primase synthesizes the first 10-ribonucleotide-long RNA primer on the leading strand and at the beginning of each Okazaki fragment on the lagging strand. Subsequently, pol α elongates such an RNA primer by incorporating about 20 deoxynucleotides, pol α displays a low processivity and, because of the lack of an intrinsic or associated 3′ → 5′ exonuclease activity, it is more error-prone than other replicative pols. Synthesis of the RNA/DNA primer catalyzed by pol α-primase is a critical step in the initiation of DNA synthesis, but little is known about the role of the DNA replication accessory proteins in its regulation. In this paper we provide evidences that the single-stranded DNA-binding protein, replication protein A (RP-A), acts as an auxiliary factor for pol α playing a dual role: (i) it stabilizes the pol α/primer complex, thus acting as a pol clamp; and (ii) it significantly reduces the misincorporation efficiency by pol α. Based on these results, we propose a hypothetical model in which RP-A is involved in the regulation of the early events of DNA synthesis by acting as a "fidelity clamp" for pol α.