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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 14 (1998), S. 905-913 
    ISSN: 0749-503X
    Keywords: carbon dioxide ; cytostasis ; G1 arrest ; meiosis ; sporulation ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Limitation of nutrients allows yeast cells to arrest proliferation at G1 phase of the cell cycle and to enter the so-called stationary phase. We show here another pathway for cytostasis, which is associated with extracellular accumulation of bicarbonate and the resulting alkalisation of medium during the proliferation of cells respiring acetate. Alkalisation of medium by addition of bicarbonate or alkaline buffers ceased proliferation at G1 phase of logarithmically growing cells and caused a severe drop in G1-cyclin (CLN1 and CLN2) mRNAs. The arrested cells were heat-shock resistant, suggesting that the cells entered the stationary phase. Cells confluently grown on acetate re-entered into the cell cycle after acidification of the culture medium. These results indicate that external alkalisation is a primary cause of the cytostasis. The alkali-induced G1 arrest was shown to be cyclic AMP (cAMP)-independent using mutant cells which lack a functional Ras/cAMP signaling pathway. Alkalisation of medium also stimulated meiosis and sporulation in rich acetate medium, confirming our previous proposal that environmental alkalisation but not nitrogen limitation is a key condition for entry into meiosis and sporulation. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 14 (1998), S. 623-631 
    ISSN: 0749-503X
    Keywords: Saccharomyces cerevisiae ; bicarbonate ; meiosis ; sporulation ; respiration ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Meiosis and sporulation in the yeast Saccharomyces cerevisiae requires social communication, mediated by an extracellular factor which is secreted from cells during sporulation and accumulates in a cell density-dependent manner. We show here genetic and biochemical analyses supporting our conclusion that the extracellular factor is bicarbonate acting as an alkali to elevate extracellular pH. Sporulation defects of mdh1 (mitochondrial malate dehydrogenase) mutants and of wild-type cells at low density were rescued extracellularly by addition of bicarbonate or other alkaline solutions to raise medium pH. Addition of bicarbonate (or alkalization of medium) raised steady-state levels of mRNA in respiration-deficient mdh1 mutants and inhibited proliferation of wild-type cells at low density. These results indicate that the two conditions (respiration competency and high cell density), required for meiosis and sporulation, are essential for extracellular accumulation of bicarbonate and resulting alkalization of medium. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 14 (1998), S. 617-622 
    ISSN: 0749-503X
    Keywords: Saccharomyces cerevisiae ; extracellular factor ; meiosis ; sporulation ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Meiosis and sporulation in the yeast Saccharomyces cerevisiae has been classically viewed as an example of unicellular, eukaryotic differentiation that occurs in response to nutritional starvation. We present evidence that S. cerevisiae produces an extracellular factor(s), called meiosis-promoting factor (MEP), that is required, in addition to starvation conditions, for efficient meiosis and sporulation. This factor is secreted and accumulates in a cell density-dependent fashion such that cells at a low density sporulate poorly under conditions in which cells at a high density sporulate efficiently. Conditioned medium from sporulating cells at a high density contains a small anionic molecule that has cytostatic activity and stimulates sporulation of cells at low density under a normal starvation condition. These results indicate that MEP-mediated social communication between cells is required for meiosis and sporulation. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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