Interaction Between Rec8 and Mis4 Is Required for Axis-Loop Chromatin Formation and Homologous Chromosome...

The Rec8 cohesin complex is required for the pairing and recombination of homologous chromosomes during meiosis, as well as for the cohesion of sister chromatids. In the fission yeast Schizosaccharomyces pombe, we previously identified a rec8-F204S mutant that lost the ability to assemble the axis-loop chromatin structure without losing sister chromatid cohesion. This mutant showed reduced meiotic recombination, indicating that pairing and recombination of homologous chromosomes require the formation of the axis-loop chromatin structure mediated by the Rec8 cohesin complex. Loading of the Rec8 cohesin complex onto chromatin is mediated by Mis4 (NIPBL in humans; Scc2 in yeast). In this study, to elucidate the functions of Mis4, we identified a mis4-LR mutant (L1150S and R1159G) that reproduced the phenotypes of the rec8-F204S mutant, which is defective in chromatin axis formation and homologous recombination while retaining sister chromatid cohesion. These mutation sites (Mis4-L1150, Mis4-R1159, and Rec8-F204) are all localized at the interaction surface between Mis4 and Rec8. Biochemical analysis revealed that the Mis4-LR mutant protein exhibited reduced Rec8-binding activity. Considering that the mis4-LR mutant phenocopied the rec8-F204S mutant, our results demonstrate that the Mis4-Rec8 interaction is required for proper formation of Rec8-dependent meiotic chromosome axis.