Homologous Recombination Independent Role For BRCA2 In Blocking Stalled Replication Fork Degradation By MRE11

Breast cancer suppressor BRCA2 is critical for the maintenance of genomic integrity and resistance to agents that damage DNA or collapse replication forks, presumably through double‐strand break repair via homologous recombination (HR). Using single‐molecule DNA fiber analysis, we show here that nascent replication tracts created before fork stalling with hydroxyurea are degraded in the absence of BRCA2 but are stable in wild‐type cells. Genetic domain and mutational analysis of BRCA2 reveals a conserved C‐terminal RAD51 binding site, which modulates the timing of mitotic entry, to be essential during fork protection, while being dispensable for HR. BRCA2 prevents chromosomal aberrations upon replication stalling, revealing an unforeseen mechanism in maintaining genomic stability distinct from HR. Both fork degradation and chromosome aberrations are alleviated by inhibition of MRE11, demonstrating a deleterious role for this nuclease at stalled forks. Thus, BRCA2 maintains genomic integrity and hence likely suppresses tumorigenesis through this novel replication‐specific function. This work was supported by the Damon Runyon Cancer Research Foundation fellowship DRG 1957‐07 to K.S. and by NIH grant R01 GM54668 to M.J.