RADX Modulates RAD51 Activity to Control Replication Fork Protection

Abstract

Summary: RAD51 promotes homologous recombination repair (HR) of double-strand breaks and acts during DNA replication to facilitate fork reversal and protect nascent DNA strands from nuclease digestion. Several additional HR proteins regulate fork protection by promoting RAD51 filament formation. Here, we show that RADX modulates stalled fork protection by antagonizing RAD51. Consequently, silencing RADX restores fork protection in cells deficient for BRCA1, BRCA2, FANCA, FANCD2, or BOD1L. Inactivating RADX prevents both MRE11- and DNA2-dependent fork degradation. Furthermore, RADX overexpression causes fork degradation that is dependent on these nucleases and fork reversal. The amount of RAD51 determines the fate of stalled replication forks, with more RAD51 required for fork protection than fork reversal. Finally, we find that RADX effectively competes with RAD51 for binding to single-stranded DNA, supporting a model in which RADX buffers RAD51 to ensure the right amount of reversal and protection to maintain genome stability. : Bhat et al. discover that RADX competes with RAD51 for ssDNA and silencing RADX confers fork protection to cells with compromised RAD51 filament stability caused by loss of BRCA1, BOD1L, and the Fanconi anemia pathway. In addition, they find that more RAD51 is needed for fork stabilization than fork reversal. Keywords: fork reversal, fork protection, RAD51, RADX, replication stress, MRE11, BRCA1, Fanconi anemia