THE REC8 GENE OF SCHIZOSACCHAROMYCES-POMBE IS INVOLVED IN LINEAR ELEMENT FORMATION, CHROMOSOME-PAIRING AND SISTER-CHROMATID COHESION DURINGMEIOSIS

The fission yeast Schizosaccharomyces pombe does not form tripartite s ynaptonemal complexes during meiotic prophase, but axial core-like str uctures (linear elements). To probe the relationship between meiotic r ecombination and the structure, pairing, and segregation of meiotic ch romosomes, we genetically and cytologically characterized the rec8-110 mutant, which is partially deficient in meiotic recombination. The pa ttern of spore viability indicates that chromosome segregation is affe cted in the mutant. A detailed segregational analysis in the rec8-110 mutant revealed more spores disomic for chromosome III than in a wild- type strain. Aberrant segregations are caused by precocious segregatio n of sister chromatids at meiosis I, rather than by nondisjunction as a consequence of lack of crossovers. In situ hybridization further sho wed that the sister chromatids are separated prematurely during meioti c prophase. Moreover, the mutant forms aberrant linear elements and sh ows a shortened meiotic prophase. Meiotic chromosome pairing in inters titial and centromeric regions is strongly impaired in rec8-110, where as the chromosome ends are less deficient in pairing. We propose that the rec8 gene encodes a protein required for linear element formation and that the different phenotypes of rec8-110 reflect direct and indir ect consequences of the absence of regular linear elements.