Abstract
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 Rad32(Mre11)) nuclease activity is required for the removal of Rec12(Spo11). Furthermore, we show that the CtIP homologue Ctp1 is required for Rec12(Spo11) removal, confirming functional conservation between Ctp1(CtIP) 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 Rec12(Spo11) removal. These observations suggest that the conserved role of the MRN complex in these meiotic functions is independent of Rec12(Spo11) removal.
Highlights
The evolutionarily conserved Mre11/Rad50/Nbs1 (MRN) complex is involved in various aspects of meiosis
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 but that all of these functions are proficient in a rad50S mutant, which is deficient for Rec12Spo11 removal
To test if the temperature-sensitive spore viability phenotype of the rad50S mutant reflects a defect in double-strand break (DSB) repair, we looked at meiotic DSB formation and repair in a meiotic time course with the rad50S strain at permissive and restrictive temperatures, using pulsed-field gel electrophoresis (Fig. 1b)
Summary
The evolutionarily conserved Mre11/Rad50/Nbs (MRN) complex is involved in various aspects of meiosis. In an S. cerevisiae rad50S point mutant (a separation-of-function mutant with severe defects in meiosis but only mild defects in mitotic DNA repair) [2], meiotic DSBs are formed, but this mutant is unable to remove Spo from meiotic DSB ends [17]. This observation has implicated the MRN complex in Spo removal. An S. pombe rad50S mutant is defective in meiotic DSB repair, and this feature has been instrumental in the study of meiotic DSB formation in this organism [42] This phenotype is compatible with an involvement of the MRN complex in Rec12Spo removal, this has not been demonstrated experimentally
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