IDENTIFICATION OF 7 NEW CUT GENES INVOLVED IN SCHIZOSACCHAROMYCES-POMBE MITOSIS

Fission yeast cut mutants cause cytokinesis in the absence of normal n uclear division. These mutants show abnormal uncoupled mitosis and are known to be the result of mutations in the genes encoding DNA topoiso merase II, proteins related to spindle pole duplication, and a kinesin -related mitotic motor. We have screened 717 temperature-sensitive (ts ) mutants by individually observing their cytological phenotypes at th e restrictive temperature, and have newly isolated 25 cut mutants. Gen etic analyses indicate that 14 of them fall into five previously ident ified loci, namely, top2, cut1, cut5, cut7 and cut9, whereas nine have been mapped onto seven new loci, designated cut13 to cut19. The cytol ogical phenotypes of the newly identified cut mutants can be classifie d into three groups. One group consists of mutants in which a portion of the nuclear chromatin is stretched by the elongated spindle but the entire nucleus is not separated, reminiscent of, but not identical to , the phenotypes of top2 and cut1; mutants cut14-208, cut15-85, cut16- 267 and cut17-275 display such a phenotype. Another group exhibits non -disjunctioned and condensed chromosomes in the presence of the spindl e, cut13-131 belongs to this group. The cut19-708 mutant has also been found to have condensed chromosomes. The remaining group has a mixed phenotype of the above two groups; namely, stretched chromatin and con densed chromosomes; cut18-447 exhibits such a phenotype. The isolation and characterization of the mutated genes will be the subjects of fut ure investigations.