Sir3 heterochromatin protein promotes non‐homologous end joining by direct inhibition of Sae2. (24th November 2021)

• Record Type: Journal Article
• Authors: Bordelet, Hélène; Costa, Rafaël; Brocas, Clémentine; Dépagne, Jordane; Veaute, Xavier; Busso, Didier; Batté, Amandine; Guérois, Raphaël; Marcand, Stéphane; Dubrana, Karine
• Is Part Of: EMBO journal. Volume 41:Number 1(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-11-24
• Subjects: DSB repair -- heterochromatin -- NHEJ -- Sae2 -- Sir3; Molecular biology -- Periodicals; 572.805
• DOI: 10.15252/embj.2021108813
• Languages: English
• ISSNs: 0261-4189

Abstract

Abstract: Heterochromatin is a conserved feature of eukaryotic chromosomes, with central roles in gene expression regulation and maintenance of genome stability. How heterochromatin proteins regulate DNA repair remains poorly described. In the yeast Saccharomyces cerevisiae, the silent information regulator (SIR) complex assembles heterochromatin‐like chromatin at sub‐telomeric chromosomal regions. SIR‐mediated repressive chromatin limits DNA double‐strand break (DSB) resection, thus protecting damaged chromosome ends during homologous recombination (HR). As resection initiation represents the crossroads between repair by non‐homologous end joining (NHEJ) or HR, we asked whether SIR‐mediated heterochromatin regulates NHEJ. We show that SIRs promote NHEJ through two pathways, one depending on repressive chromatin assembly, and the other relying on Sir3 in a manner that is independent of its heterochromatin‐promoting function. Via physical interaction with the Sae2 protein, Sir3 impairs Sae2‐dependent functions of the MRX (Mre11‐Rad50‐Xrs2) complex, thereby limiting Mre11‐mediated resection, delaying MRX removal from DSB ends, and promoting NHEJ. Synopsis: During homologous recombination repair, the Sae2 protein stimulates MRX complex‐dependent initiation of DNA double‐strand break (DSB) resection. Here, the budding yeast heterochromatin protein Sir3 is found to directly bind Sae2 and inhibit its resection function at DSBs both in heterochromatin and euchromatin. The Sae2 C‐terminus physically interacts with the N‐terminal part of the Sir3 AAA+ domain (Sir3SaID). Sae2 and Sir4 compete for Sir3 binding. The sir3‐T557I mutation impairs Sir3‐Sae2 interaction. Sir3‐Sae2 interaction is sufficient to inhibit Sae2‐mediated stimulation of Mre11 endonuclease activity. Abstract : SIR‐mediated repressive chromatin protects damaged yeast chromosomes from unscheduled homologous recombination by directly suppressing endonuclease‐dependent initation of DNA double‐strand break resection.