Figure 1.

DSB end resection in checkpoint signaling and presynaptic filament assembly. DSBs are processed nucleolytically to expose 3′ ssDNA tails that are immediately bound by RPA. The RPA-coated ssDNA recruits the ATR–ATRIP complex, leading to the activation of ATR and downstream effectors such as Chk1 to initiate the checkpoint signaling cascade. For HR repair to occur, RPA is dislodged from the ssDNA and replaced by Rad51 with the assistance of recombination mediator proteins, such as BRCA2, to form the presynaptic filament.