Replication protein A promotes 5'-->3' end processing during homology-dependent DNA double-strand break repair

Replication protein A (RPA), the eukaryotic single-strand deoxyribonucleic acid (DNA [ss-DNA])-binding protein, is involved in DNA replication, nucleotide damage repair, mismatch repair, and DNA damage checkpoint response, but its function in DNA double-strand break (DSB) repair is poorly understood. We investigated the function of RPA in homology-dependent DSB repair using Xenopus laevis nucleoplasmic extracts as a model system. We found that RPA is required for single-strand annealing, one of the homology-dependent DSB repair pathways. Furthermore, RPA promotes the generation of 3' single-strand tails (ss-tails) by stimulating both the Xenopus Werner syndrome protein (xWRN)-mediated unwinding of DNA ends and the subsequent Xenopus DNA2 (xDNA2)-mediated degradation of the 5' ss-tail. Purified xWRN, xDNA2, and RPA are sufficient to carry out the 5'-strand resection of DNA that carries a 3' ss-tail. These results provide strong biochemical evidence to link RPA to a specific DSB repair pathway and reveal a novel function of RPA in the generation of 3' ss-DNA for homology-dependent DSB repair.