Figure 7.

Proposed model for the role of ATM in HR. ATM is indeed required for the presynapsis stage of HR: (i) to phosphorylate and remove KAP1, facilitating the recruitment of HR proteins; (ii) to regulate the end resection step by stimulating the nucleolytic activity of MRE11/CtIP to generate 3′-ssDNA overhangs and facilitate RAD51 nucleofilament formation; (iii) in addition, we describe here for the first time that ATM is also required for HR after RAD51 nucleofilament formation. In the absence of ATM, ATR can only participate in the early steps of HR, possibly through the stimulation of end resection and RAD51 nucleofilament formation.