A genome-wide homologous recombination screen identifies the RNA-binding protein RBMX as a component of the DNA damage response

Repair of DNA double strand breaks is critical to genomic stability and the prevention of developmental disorders and cancer. A central pathway for this repair is homologous recombination (HR). Most knowledge of HR is derived from work in prokaryotic and eukaryotic model organisms. We performed a genome-wide siRNA-based screen in human cells. Among positive regulators of HR we identified networks of DNA damage response and pre-mRNA processing proteins, and among negative regulators we identified a phosphatase network. Three candidate proteins localized to DNA lesions including RBMX, a heterogeneous nuclear ribonucleoprotein that has a role in alternative splicing. RBMX accumulated at DNA lesions via multiple domains in a poly(ADP-ribose) polymerase 1-dependent manner and promoted HR by facilitating proper BRCA2 expression. Our screen also revealed that off-target depletion of Rad51 is a common source of RNAi false-positives, sounding a cautionary note for siRNA screens and RNAi-based studies of HR.