Nej1XLFinteracts with Sae2CTIPto inhibit Dna2 mediated resection at DNA double strand break

The two major pathways of DNA double strand break (DSB) repair, non-homologous end-joining (NHEJ) and homologous recombination (HR), are highly conserved from yeast to mammals. The regulation of 5’ DNA resection controls repair pathway choice and influences repair outcomes. Nej1 was first identified as a canonical NHEJ factor involved in stimulating the ligation of broken DNA ends and more recently, it was shown to be important for DNA end-bridging and inhibiting 5’ resection mediated by Dna2-Sgs1. Nej1 interacts with Sae2 and this impacts DSB repair in three ways. First, Nej1 inhibits MRX-Sae2 interactions and Sae2 localization to a DSB. Second, Nej1 inhibits Sae2-dependent recruitment of Dna2 in the absence of Sgs1. Third, NEJ1 and SAE2 showed an epistatic relationship for DNA end-bridging, an event that restrains the broken ends and reduces the frequency of genomic deletions from developing at the DSB. Deletion of NEJ1 suppressed the synthetic lethality of sae2 Δ sgs1 Δ and was dependent on the nuclease activity of Dna2. These Nej1 functions promote end-joining DSB repair, but could also be relevant for controlling resection initiation during HR repair. Highlights Nej1 physically interacts with Sae2 and inhibits end-resection at a DSB. Nej1 inhibits Sae2 interactions with the MRX complex. Nej1 inhibits Sae2-dependent recruitment of Dna2 to a DSB. NEJ1 and SAE2 are epistatic for DNA end-bridging. Deletion of NEJ1 suppresses the synthetic lethality of sae2 Δ sgs1 Δ, which is dependent on Dna2 nuclease activity.