Biochemical and genetic analyses of the role of yeast casein kinase 2 in salt tolerance.
Saccharomyces cerevisiae cells lacking the regulatory subunit of casein kinase 2 (CK-2), encoded by the gene CKB1, display a phenotype of hypersensitivity to Na(+) and Li(+) cations. The sensitivity of a strain lacking ckb1 is higher than that of a calcineurin mutant and similar to that of a strain lacking HAL3, the regulatory subunit of the Ppz1 protein phosphatase. Genetic analysis indicated that Ckb1 participates in regulatory pathways different from that of Ppz1 or calcineurin. Deletion of CKB1 increased the salt sensitivity of a strain lacking Ena1 ATPase, the major determinant for sodium efflux, suggesting that the function of the kinase is not mediated by Ena1. Consistently, ckb1 mutants did not show an altered cation efflux. The function of Ckb1 was independent of the TRK system, which is responsible for discrimination of potassium and sodium entry, and in the absence of the kinase regulatory subunit, the influx of sodium was essentially normal. Therefore, the salt sensitivity of a ckb1 mutant cannot be attributed to defects in the fluxes of sodium. In fact, in these cells, both the intracellular content and the cytoplasm/vacuole ratio for sodium were similar to those features of wild-type cells. The possible causes for the salt sensitivity phenotype of casein kinase mutants are discussed in the light of these findings.
de Nadal
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E
Departamento Bioquímica i Biologia Molecular, Universitat Autònoma de Barcelona, Bellaterra 08193, Barcelona, Spain.
Calero
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F
Ramos
J
J
Ariño
J
J
D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism; D001692:Biological Transport; D019703:Calcineurin / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D047390:Casein Kinase II; D027682:Cation Transport Proteins; D002414:Cations, Monovalent / Q000378:metabolism / Q000633:toxicity; D018797:Cell Cycle Proteins; D004352:Drug Resistance, Microbial; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D008094:Lithium / Q000378:metabolism / Q000633:toxicity*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D009708:Nucleotidases / Q000235:genetics / Q000378:metabolism; D010641:Phenotype; D010749:Phosphoprotein Phosphatases / Q000235:genetics / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins; D012964:Sodium / Q000378:metabolism / Q000633:toxicity*; D000254:Sodium-Potassium-Exchanging ATPase
D002352:Carrier Proteins; D027682:Cation Transport Proteins; D002414:Cations, Monovalent; D018797:Cell Cycle Proteins; C086375:ENA1 protein, S cerevisiae; D005656:Fungal Proteins; D008565:Membrane Proteins; C092936:SIS2 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C085258:TRK2 protein, S cerevisiae; C068664:TRK1 protein, S cerevisiae; D008094:Lithium; D012964:Sodium; D047390:Casein Kinase II; D017346:Protein Serine-Threonine Kinases; D009708:Nucleotidases; D019703:Calcineurin; C075119:PPZ1 protein, S cerevisiae; D010749:Phosphoprotein Phosphatases; C053354:bisphosphoadenylate 3'-nucleotidase; D000251:Adenosine Triphosphatases; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium