|Budget Amount *help
¥2,600,000 (Direct Cost : ¥2,600,000)
Fiscal Year 1997 : ¥1,200,000 (Direct Cost : ¥1,200,000)
Fiscal Year 1996 : ¥1,400,000 (Direct Cost : ¥1,400,000)
One essential function in the cell cycle is the equal division of chromosomes into the mother and the daughter cell. In the budding yeast Saccharomyces cerevisiae, nuclear DNA replicated in the mother cell migrates to the mother-daughter junction by uni-polar movement towards the daughter bud in concert with bud emergence and spindle duplication, and then the nucleus is pulled by bi-polar mode and divided to two nuclear lobes in the mother and the daughter cell during mitosis. Accompanied by this nuclear movement, different mitotic cyclins are successively associated with Cdc28 kinase during mitosis in the cell cycle. To address the function of mitotic cyclins in nuclear movement prior to division, we analyzed the effects of mitotic cyclins on behavior of the nucleus in budding yeast.
On overproducing vertebrate cyclin Al in the yeast, the nucleus failed to divide correctly and the majority of chromosomes were found in the daughter bud, instead of dividing into the mother and the daught
er cells. Endogenous mitotic cyclin Clb3 produced the same phenotypes, whereas Gl cyclin Cln2 did not. Concomitantly, short mitotic spindles and two SPBs entered into the daughter bud, and cytoplasmic spindles showed an aberrant morphology in the mother cell rather than in the daughter. This phenotype was observed by producing an indestructible cyclin mutant, but not by a mutated cyclin unable to activate Cdc28 kinase. These results suggset that the aberrant nuclear movement induced by mitotic cyclin cyclin A,as well as Clb3, may result from an altered spindle function. The process of nuclear movement and the spindle transition prior to division might be regulated by cyclin A-mediated Cdc28 kinase and its cyclin degradation.
We isolated the mutants that can rescue the growth arrest caused by cyclin A expression in the budding yeast, and identified the four genes, which can interact which cyclin A-Cdc28 complex, a new allele of CDC28, DEAD1, YDJ1, a novel ubiquitin-related gene. We need more analysis of these factors at the molecular level in cell cycle regulation.