Identification of protein kinase disruptions as suppressors of the calcium sensitivity of S. cerevisiae Deltaptp2 Deltamsg5 protein phosphatase double disruptant.

The double disruptant of the S. cerevisiae protein phosphatase (PPase) genes, PTP2 (phosphotyrosine-specific PPase) and MSG5 (phosphotyrosine and phosphothreonine/serine-PPase) causes calcium-sensitive growth (Cas). Previous study using Fluorescent-activated cell sorting (FACS) analysis showed that this growth defect with calcium occurs at G1-S transition in the cell cycle. We discovered that six non-essential protein kinase (PKase) disruptions (Deltabck1, Deltamkk1, Deltaslt2/Deltampk1, Deltamck1, Deltassk2 and Deltayak1) suppressed the Cas-phenotype of the Deltaptp2 Deltamsg5 double disruptant. Bck1p, Mkk1p and Slt2p are components of the mitogen-activated protein kinase (MAPK) cascade of cell wall integrity pathway (Slt2 pathway), and Mck1p is its down regulator. Ssk2p is the MAPK kinase kinase of the high-osmolarity glycerol (HOG) pathway, while Yak1p is a negative regulator for the cAMP-dependent pathway. FACS analysis revealed that only the disruption of Deltassk2 and Deltayak1 but not Deltabck1, Deltamkk1, Deltaslt2 and Deltamck1 was able to suppress the delayed G1-S transition, suggesting that suppression of the growth defect is not always accompanied by suppression of the G1-S transition delay. The discovery of these PKases as suppressors revealed that in addition to the previously anticipated Slt2 pathway, HOG, Yak1p and Mck1p regulatory pathways may also be involved in the calcium sensitivity of the Deltaptp2 Deltamsg5 double disruptant.

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