SAE2 is a protein involved in repairing meiotic and mitotic double-strand breaks in DNA. It has been shown to negatively regulate DNA damage checkpoint signalling [1,2]. SAE2 is homologous to the CtIP proteins in mammals and an homologous protein in plants. Crucial sequence motifs that are highly conserved are the CxxC and the RHR motifs in this C-terminal part of the protein [3]. In budding yeast, genetic evidence suggests that the SAE2 protein is essential for the processing of hairpin DNA intermediates and meiotic double-strand breaks by Mre11/Rad50 complexes. SAE2 binds DNA and exhibits endonuclease activity on single-stranded DNA independently of Mre11/Rad50 complexes, but hairpin DNA structures are cleaved cooperatively in the presence of Mre11/Rad50 or Mre11/Rad50/Xrs2. Hairpin structures are not processed at the tip by SAE2 but rather at single-stranded DNA regions adjacent to the hairpin. The catalytic activities of SAE2 are important for its biological functions [6]. Although proteins containing this domain were described as endonucleases, it is now known that they actually function as endonuclease activators [7]. This domain contains highly conserved residues at its 15-residue extreme that are indispensable for MRN (Mre11-Rad50-Nbs1) complex activation, through the stimulation of Mre11 endonuclease activity [7].

1: The Saccharomyces cerevisiae Sae2 protein negatively regulates DNA damage checkpoint signalling. Clerici M, Mantiero D, Lucchini G, Longhese MP; EMBO Rep. 2005; [Epub ahead of print] PMID:16374511

2: The Saccharomyces cerevisiae Sae2 protein promotes resection and bridging of double strand break ends. Clerici M, Mantiero D, Lucchini G, Longhese MP; J Biol Chem. 2005;280:38631-38638. PMID:16162495

3: Ctp1 is a cell-cycle-regulated protein that functions with Mre11 complex to control double-strand break repair by homologous recombination. Limbo O, Chahwan C, Yamada Y, de Bruin RA, Wittenberg C, Russell P; Mol Cell. 2007;28:134-146. PMID:17936710

4: A conserved function for a Caenorhabditis elegans Com1/Sae2/CtIP protein homolog in meiotic recombination. Penkner A, Portik-Dobos Z, Tang L, Schnabel R, Novatchkova M, Jantsch V, Loidl J; EMBO J. 2007;26:5071-5082. PMID:18007596

5: A novel plant gene essential for meiosis is related to the human CtIP and the yeast COM1/SAE2 gene. Uanschou C, Siwiec T, Pedrosa-Harand A, Kerzendorfer C, Sanchez-Moran E, Novatchkova M, Akimcheva S, Woglar A, Klein F, Schlogelhofer P; EMBO J. 2007; [Epub ahead of print] PMID:18007598

6: Sae2 is an endonuclease that processes hairpin DNA cooperatively with the Mre11/Rad50/Xrs2 complex. Lengsfeld BM, Rattray AJ, Bhaskara V, Ghirlando R, Paull TT; Mol Cell. 2007;28:638-651. PMID:18042458

7: A conserved Ctp1/CtIP C-terminal peptide stimulates Mre11 endonuclease activity. Zdravkovic A, Daley JM, Dutta A, Niwa T, Murayama Y, Kanamaru S, Ito K, Maki T, Argunhan B, Takahashi M, Tsubouchi H, Sung P, Iwasaki H; Proc Natl Acad Sci U S A. 2021; [Epub ahead of print] PMID:33836577