Replication protein a as a "fidelity clamp" for DNA polymerase alpha

The current view of DNA replication in eukaryotes predicts that DNA polymer ase alpha (pol alpha)-primase synthesizes the first 10-ribonucleotide-long RNA primer on the leading strand and at the beginning of each Okazaki fragm ent on the lagging strand. Subsequently, pol alpha elongates such an RNA pr imer by incorporating about 20 deoxynucleotides. pol alpha displays a low p rocessivity 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 alpha -primase is a critic al step in the initiation of DNA synthesis, but little is known about the r ole of the DNA replication accessory proteins in its regulation. In this pa per we provide evidences that the single-stranded DNA-binding protein, repl ication protein A (RP-A), acts as an auxiliary factor for pol alpha playing a dual role: (i) it stabilizes the pol alpha /primer complex, thus acting as a pol clamp; and (ii) it significantly reduces the misincorporation effi ciency by pol alpha. Based on these results, we propose a hypothetical mode l in which RP-A is involved in the regulation of the early events of DNA sy nthesis by acting as a "fidelity clamp" for pol alpha.