Breast Cancer Proteins PALB2 and BRCA2 Stimulate Polymerase h in Recombination-Associated DNA Synthesis at Blocked Replication Forks

One envisioned function of homologous recombination (HR) is to find a template for DNA synthesis from the resected 3 '-OH molecules that occur during double-strand break (DSB) repair at collapsed replication forks. However, the interplay between DNA synthesis and HR remains poorly understood in higher eukaryotic cells. Here, we reveal functions for the breast cancer proteins BRCA2 and PALB2 at blocked replication forks and show a role for these proteins in stimulating polymerase h (Polh) to initiate DNA synthesis. PALB2, BRCA2, and Pol eta colocalize at stalled or collapsed replication forks after hydroxyurea treatment. Moreover, PALB2 and BRCA2 interact with Polh and are required to sustain the recruitment of Polh at blocked replication forks. PALB2 and BRCA2 stimulate Polh-dependent DNA synthesis on D loop substrates. We conclude that PALB2 and BRCA2, in addition to their functions in D loop formation, play crucial roles in the initiation of recombination-associated DNA synthesis by Pol eta-mediated DNA repair.