Cell cycle regulation by Ca2+ and its physiological role in yeast

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To investigate cell cycle regulation by Ca2+ signaling in the yeast Saccharomyces cerevisiae, we isolated many mutants defective in this process and molecular genetic analysis of each mutant was performed. Major outcome are as follows.(1)The isolation of the mutants and their genetic characterization.In addition to the previously characterized 15 complementation groups we further identified 7 new complementation groups to have 22 groups in total.(2)Molecular genetic characterization of scz13 mutant :scz13 mutation was identified as an allele of SAH1 gene that encodes S-adenosylhomocystein (AdoHcy) hydrolase. We have demonstrated that the cellular levels of AdoHcy and its precursor S-adenosylmethionine were highly elevated and cell growth of this mutant was arrested in G1 phase. Due to the elevation of cellular levels of AdoHcy and AdoMet, the expression levels of CLN2 and SWE1 were strongly suppressed. The results indicated the involvement of AdoHcy and AdoMet in cell cycle regulation. … More (3)Molecular genetic characterization of scz13 mutant :scz6 mutation was identified as an allele of a unique PKC1 gene that encodes protein kinase C in yeast. Pkc1 of yeast is known to be involved in the regulation of Mpk1 MAP kinase cascade, which regulates the synthesis of cell wall. We have shown that the defect of scz6 mutant was in the function different from the previously known Pkc1 function. The novel Pkc1 function is required for the expression of Cln2 G1 cyclin which leading to actin polarization polymerization which in turn leads to polar cell growth.(4)Growth regulation that involves calcineurin.We found that calcineurin and high osmolarity glycerol (HOG) pathway antagonize in the regulation of cell growth. More specifically, calcineurin is required for the inhibition of actin polarization at the bud site, and HOG pathway is required for the positive regulation of the formation of the bud after actin has polarized. This mechanism is required for the regulation of bud formation under the conditions of the changes in osmolarity of the environment. Less