ATM / ATR ‐mediated phosphorylation of PALB 2 promotes RAD 51 function

DNA damage activates the ATM and ATR kinases that coordinate checkpoint and DNA repair pathways. An essential step in homology‐directed repair ( HDR ) of DNA breaks is the formation of RAD 51 nucleofilaments mediated by PALB 2– BRCA 2; however, roles of ATM and ATR in this critical step of HDR are poorly understood. Here, we show that PALB 2 is markedly phosphorylated in response to genotoxic stresses such as ionizing radiation and hydroxyurea. This response is mediated by the ATM and ATR kinases through three N‐terminal S/Q ‐sites in PALB 2, the consensus target sites for ATM and ATR . Importantly, a phospho‐deficient PALB 2 mutant is unable to support proper RAD 51 foci formation, a key PALB 2 regulated repair event, whereas a phospho‐mimicking PALB 2 version supports RAD 51 foci formation. Moreover, phospho‐deficient PALB 2 is less potent in HDR than wild‐type PALB 2. Further, this mutation reveals a separation in PALB 2 function, as the PALB 2‐dependent checkpoint response is normal in cells expressing the phospho‐deficient PALB 2 mutant. Collectively, our findings highlight a critical importance of PALB 2 phosphorylation as a novel regulatory step in genome maintenance after genotoxic stress.