Ctp1CtIP and the Rad32Mre11 nuclease activity are required for Rec12Spo11 removal but Rec12Spo11 removal is dispensable for other MRN-dependent meiotic functions

The evolutionarily conserved Mre11/Rad50/Nbs1 (MRN) complex is involved in various aspects of meiosis. Whereas available evidence suggests that the Mre11 nuclease activity might be responsible for Spo11 removal in Saccharomyces cerevisiae, this has not been confirmed experimentally. This study demonstrates for the first time that Mre11 (Schizosaccharomyces pombe Rad32Mre11) nuclease activity is required for the removal of Rec12Spo11. Furthermore, we show that the CtIP homologue Ctp1 is required for Rec12Spo11 removal, confirming functional conservation between Ctp1CtIP and the more distantly related Sae2 protein from Saccharomyces cerevisiae. Finally, we show that the MRN complex is required for meiotic recombination, chromatin remodeling at the ade6-M26 recombination hot spot, and formation of linear elements (which are the equivalent of the synaptonemal complex found in other eukaryotes) but that all of these functions are proficient in a rad50S mutant, which is deficient for Rec12Spo11 removal. These observations suggest that the conserved role of the MRN complex in these meiotic functions is independent of Rec12Spo11 removal.