title: The Ppz protein phosphatases regulate Trk-independent potassium influx in yeast.
abstract: The Ppz protein phosphatases have been recently shown to negatively regulate the major potassium transport system in the yeast Saccharomyces cerevisiae, encoded by the TRK1 and TRK2 genes. We have found that, in the absence of the Trk system, Ppz mutants require abnormally high concentrations of potassium to proliferate. This can be explained by the observation that trk1 trk2 ppz1 or trk1 trk2 ppz1 ppz2 strains display a very poor rubidium uptake, with markedly increased Km values. These cells are very sensitive to the presence of several toxic cations in the medium, such as hygromicyn B or spermine, but not to lithium or sodium cations. At limiting potassium concentrations, addition of EGTA to the medium improves growth of these mutants. Therefore, our results indicate that, in addition to their role in regulating Trk potassium transporters, Ppz phosphatases (essentially Ppz1), positively affect the residual low affinity potassium transport mechanisms in yeast. These findings may provide a new way to elucidate the molecular nature of the low affinity potassium uptake system in yeast as well as a useful model to analyze the function of plant or mammalian potassium channels through heterologous expression in yeast.
authors.affiliation: Departament de Bioquímica i Biologia Molecular, Universitat Autónoma de Barcelona, Bellaterra 08193, Barcelona, Spain.
authors.forename: Amparo
authors.initials: A
authors.lastname: Ruiz
authors.forename: María
authors.initials: M
authors.lastname: del Carmen Ruiz
authors.forename: Miguel Angel
authors.initials: MA
authors.lastname: Sánchez-Garrido
authors.forename: Joaquín
authors.initials: J
authors.lastname: Ariño
authors.forename: José
authors.initials: J
authors.lastname: Ramos
mesh_terms: D002118:Calcium / Q000378:metabolism; D027682:Cation Transport Proteins / Q000235:genetics / Q000378:metabolism*; D002412:Cations / Q000633:toxicity; D009154:Mutation; D010749:Phosphoprotein Phosphatases / Q000235:genetics / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D012413:Rubidium / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D027682:Cation Transport Proteins; D002412:Cations; D029701:Saccharomyces cerevisiae Proteins; C085258:TRK2 protein, S cerevisiae; C068664:TRK1 protein, S cerevisiae; C075119:PPZ1 protein, S cerevisiae; C082731:PPZ2 protein, S cerevisiae; D010749:Phosphoprotein Phosphatases; D012413:Rubidium; D011188:Potassium; D002118:Calcium