In Saccharomyces cerevisiae, the Mre11-Rad50-Xrs2 (MRX) protein complex plays pivotal roles in double-strandbreak (DSB) repair, replication stress and telomere length maintenance. Another protein linked to DSB repair is Sae2,which regulates MRX persistence at DSBs. However, very little is known about its role in DNA replication stress andrepair. Here, we reveal a crucial role for Sae2 in DNA replication stress. We show that different mutant alleles of SAE2cause hypersensitivity to genotoxic agents, and when combined with Δmre11 or nuclease-defective mre11 mutantalleles, the double mutants are considerably more sensitive suggesting that the sae2 mutations synergize with mre11mutations. Biochemical studies demonstrate that Sae2 exists as a dimer in solution, associates preferentially withsingle-stranded and branched DNA structures, exhibits structure-specific endonuclease activity and cleaves thesesubstrates from the 5′ end. Furthermore, we show that the nuclease activity is indeed intrinsic to Sae2. Interestingly,sae2G270D protein possesses DNA-binding activity, but lacks detectable nuclease activity. Altogether, our data suggesta direct role for Sae2 nuclease activity in processing of the DNA structures that arise during replication and DNAdamage and provide insights into the mechanism underlying Mre11-Sae2-mediated abrogation of replication stress-relateddefects in S. cerevisiae.
Volume 45, 2020
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