The canonical role of cohesin is to mediate sister chromatid cohesion. In addition, cohesin plays important roles in processes such as DNA repair and regulation of gene expression. Mounting evidence suggests that various post-translational modifications, including phosphorylation, acetylation and sumoylation regulate cohesin functions. Our mass spectrometry analysis of cohesin purified from Schizosaccharomyces pombe cells revealed that the cohesin subunit Psm1 is methylated on two evolutionarily conserved lysine residues, K536 and K1200. We found that mutations that prevent methylation of Psm1 K536 and K1200 render sensitivity to DNA-damaging agents and show positive genetic interactions with mutations in genes encoding the Mus81–Eme1 endonuclease. Yeast two-hybrid and co-immunoprecipitation assays showed that there were interactions between subunits of the cohesin and Mus81–Eme1 complexes. We conclude that cohesin is methylated and that mutations that prevent methylation of Psm1 K536 and K1200 show synthetic phenotypes with mutants defective in the homologous recombination DNA repair pathway.

SummaryOne of the key features of meiosis is that shugoshin in complex with protein phosphatase 2A (PP2A) protects centromeric cohesin during meiosis I, but not during meiosis II. A new model suggests that a PP2A inhibitor mediates deprotection of centromeric cohesin during meiosis II.

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Targeted protein degradation systems developed for eukaryotes employ cytoplasmic machineries to perform proteolysis. This has prevented mitochondria-specific analysis of genome maintaining proteins that localize to both mitochondria and nucleus. Here, we present an inducible mitochondria-specific protein degradation system in Saccharomyces cerevisiae based on the Mesoplasma florum Lon (mf-Lon) protease and its corresponding ssrA tag (called PDT). We show that mitochondrially targeted mf-Lon protease efficiently and selectively degrades a PDT- tagged reporter protein localized to the mitochondrial matrix. The degradation can be induced by depleting adenine from the medium and tuned by altering the promoter strength of the MF-LON gene. Finally, we demonstrate that mf-Lon degrades endogenous, dually localized proteins inside mitochondria. In summary, our system is an efficient tool for analysis of intricate mitochondria-nuclear crosstalk essential for proper mitochondrial function.