DNA repair protein endonuclease SAE2/CtIP C-terminus
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. 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. It is now known to be an endonuclease. 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.