Endonuclease that cooperates with the MRN complex in processing meiotic and mitotic double-strand breaks by allowing the endonucleolytic removal of rec12 from the break sites and ensuring both resection and intrachromosomal association of the broken ends. Required for the formation of RPA-coated single strand DNA adjacent to the DSBs where it functions together with the MRN complex in 5'- 3' resection. Required for the repair of programmed meiotic DSBs. Involved also in an rhp51 recombinase-dependent recombinational repair pathway. Accumulates at DSBs. Phosphorylated by tel1 in response to DNA damage. Belongs to the COM1/SAE2/CtIP family.