title: Characterization of potassium transport in wild-type and isogenic yeast strains carrying all combinations of trk1, trk2 and tok1 null mutations.
abstract: Saccharomyces cerevisiae cells express three defined potassium-specific transport systems en-coded by TRK1, TRK2 and TOK1. To gain a more complete understanding of the physiological function of these transport proteins, we have constructed a set of isogenic yeast strains carrying all combinations of trk1delta, trk2delta and tok1delta null mutations. The in vivo K+ transport characteristics of each strain have been documented using growth-based assays, and the in vitro biochemical and electrophysiological properties associated with K+ transport have been determined. As has been reported previously, Trk1p and Trk2p facilitate high-affinity potassium uptake and appear to be functionally redundant under a wide range of environmental conditions. In the absence of TRK1 and TRK2, strains lack the ability specifically to take up K+, and trk1deltatrk2delta double mutant cells depend upon poorly understood non-specific cation uptake mechanisms for growth. Under conditions that impair the activity of the non-specific uptake system, termed NSC1, we have found that the presence of functional Tok1p renders cells sensitive to Cs+. Based on this finding, we have established a growth-based assay that monitors the in vivo activity of Tok1p.
authors.affiliation: Universität Karlsruhe, Germany.
authors.forename: Adam
authors.initials: A
authors.lastname: Bertl
authors.forename: José
authors.initials: J
authors.lastname: Ramos
authors.forename: Jost
authors.initials: J
authors.lastname: Ludwig
authors.forename: Hella
authors.initials: H
authors.lastname: Lichtenberg-Fraté
authors.forename: John
authors.initials: J
authors.lastname: Reid
authors.forename: Hermann
authors.initials: H
authors.lastname: Bihler
authors.forename: Fernando
authors.initials: F
authors.lastname: Calero
authors.forename: Paula
authors.initials: P
authors.lastname: Martínez
authors.forename: Per O
authors.initials: PO
authors.lastname: Ljungdahl
mesh_terms: D001692:Biological Transport; D027682:Cation Transport Proteins / Q000235:genetics / Q000378:metabolism; D002412:Cations / Q000378:metabolism; D003470:Culture Media; D004594:Electrophysiology; D005800:Genes, Fungal; D009154:Mutation; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000235:genetics / Q000378:metabolism; D012413:Rubidium / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics* / Q000378:metabolism*
chemical_list: D027682:Cation Transport Proteins; D002412:Cations; D003470:Culture Media; D015221:Potassium Channels; D029701:Saccharomyces cerevisiae Proteins; C095220:TOK1 protein, S cerevisiae; C085258:TRK2 protein, S cerevisiae; C068664:TRK1 protein, S cerevisiae; D012413:Rubidium; D011188:Potassium