Human BRCA2 protein promotes RAD51 filament formation on RPA-covered single-stranded

BRCA2 is an important tumor suppressor and functions in homologous recombination, a key genomic integrity pathway. BRCA2 interacts with RAD51, the central protein of recombination, which forms filaments on ssDNA to perform homology search and DNA strand invasion. We report the purification of full-length human BRCA2, and show that it binds to ~6 RAD51 molecules and promotes RAD51 binding to RPA-covered ssDNA in a manner that is stimulated by DSS1. Germline mutations in the BRCA2 gene confer a highly elevated lifetime risk of developing breast, ovarian, and other cancers 1. The tumor suppressor function relates to a role of BRCA2 protein in homologous recombination 2, but the mechanistic analysis of human BRCA2 has been impeded by difficulties purifying this large protein (3,418 amino acids). BRCA2 contains 8 conserved BRC repeats and a C-terminal region that bind RAD51 with varying affinity 3,4 and is required for RAD51 localization to sites of DNA damage 5. RAD51 filament formation on ssDNA is inhibited by the binding of the ssDNA-binding protein RPA to the substrate. Filament formation requires the action of mediator proteins 6