The 9-1-1 Complex Controls Mre11 Nuclease and Checkpoint Activation during Short-Range Resection of DNA Double-Strand Breaks

Resection of DNA double-strand breaks is a two-step process that relies on short and long-range nucleases. Gobbini et al. show that the 9-1-1 complex plays a dual function during short-range resection, promoting checkpoint activation by recruiting Rad9 at damaged sites and negatively regulating short-range resection in a Rad9-independent manner by restricting Mre11 nuclease. © 2020 The Author(s) Homologous recombination is initiated by nucleolytic degradation (resection) of DNA double-strand breaks (DSBs). DSB resection is a two-step process in which an initial short-range step is catalyzed by the Mre11-Rad50-Xrs2 (MRX) complex and limited to the vicinity of the DSB end. Then the two long-range resection Exo1 and Dna2-Sgs1 nucleases extend the resected DNA tracts. How short-range resection is regulated and contributes to checkpoint activation remains to be determined. Here, we show that abrogation of long-range resection induces a checkpoint response that decreases DNA damage resistance. This checkpoint depends on the 9-1-1 complex, which recruits Dpb11 and Rad9 at damaged DNA. Furthermore, the 9-1-1 complex, independently of Dpb11 and Rad9, restricts short-range resection by negatively regulating Mre11 nuclease. We propose that 9-1-1, which is loaded at the leading edge of resection, plays a key function in regulating Mre11 nuclease and checkpoint activation once DSB resection is initiated.