IDENTIFICATION OF CUT8(-KINASE GENE, WHICH COMPLEMENT A FISSION YEASTMUTATION THAT BLOCKS ANAPHASE() AND CEK1(+), A NOVEL PROTEIN)

The fission yeast Schizosaccharomyces cerevisiae temperature sensitivi ty cut8-563 mutation causes chromosome overcondensation and short spin dle formation in the absence of sister chromatid separation. The cut8- 563 mutation allows cytokinesis before the completion of anaphase, thu s producing cells with a cut phenotype. The cut8(+) gene product may b e required for normal progression of anaphase. Diploidization occurs a t the restrictive temperature, and 60 to 70% of the cells surviving af ter two generations are diploid. These phenotypes are reminiscent of t hose of budding yeast (Saccharomyces cerevisiae) ctf13 and ctf14 (ndc1 0) mutations. The cut8(+) gene, isolated by complementation of the mut ant, predicts a 262-amino-acid protein; the amino and carboxy domains are hydrophilic, while the central domain contains several hydrophobic stretches. It has a weak overall similarity to the budding yeast DBF8 gene product. DBF8 is an essential gene whose mutations result in del ay in mitotic progression and chromosome instability. Anti-cuts antibo dies detect a 33-kDa polypeptide. Two multicopy suppressor genes for c ut8-563 are identified. They are the cut1(+) gene essential for nuclea r division, and a new gene (designated cek1(+)) which encodes a novel protein kinase. The cek1(+) gene product is unusually large (1,309 ami no acids) and has a 112-amino-acid additional sequence in the kinase d omain. The cek1(+) gene is not an essential gene. Protein phosphorylat ion by cek1 may facilitate the progression of anaphase through direct or indirect interaction with the cuts protein.