title: The SpTRK gene encodes a potassium-specific transport protein TKHp in Schizosaccharomyces pombe.
abstract: Complementary DNAs involved in potassium transport in Schizosaccharomyces pombe were selected by complementation of defective K+ uptake in a trk1 trk2 mutant of Saccharomyces cerevisiae. Here we describe the SpTRK gene that encodes a protein of 833 amino acids. The predicted structure contains 12 putative membrane-spanning domains and resembles various high- and low-affinity systems for K+ transport in yeasts and plants. TKHp, the product of SpTRK exhibits high homology to TRK1 and TRK2 of Saccharomyces cerevisiae as well as to HKT1 of Triticum aestivum, but is not related to HAK1 of another ascomycete, Schwanniomyces occidentalis, suggesting that different routes for potassium uptake evolved independently. This protein is a potassium-specific transporter since functional analysis of the SpTRK complemented mutant strain of Sacch. cerevisiae revealed potassium transport affinities and uptake characteristics similar to those obtained in wild-type Sch. pombe. Patch-clamp analysis in the whole-cell mode confirmed the TKHp-mediated inward current in the complemented strain. The inward current increased by acidification of the extracellular medium thereby suggesting a mechanism of K+H+ cotransport. The inward current is not detectable when external K+ is substituted by Na+, documenting a distinct cation specificity of the protein.
authors.affiliation: Botanisches Institut der Universität Bonn, 53115 Bonn, FRG.
authors.forename: H
authors.initials: H
authors.lastname: Lichtenberg-Fraté
authors.forename: J D
authors.initials: JD
authors.lastname: Reid
authors.forename: M
authors.initials: M
authors.lastname: Heyer
authors.forename: M
authors.initials: M
authors.lastname: Höfer
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D027682:Cation Transport Proteins; D018076:DNA, Complementary / Q000235:genetics; D005656:Fungal Proteins / Q000235:genetics* / Q000378:metabolism; D005800:Genes, Fungal; D005816:Genetic Complementation Test; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism*; D011487:Protein Conformation; D012441:Saccharomyces cerevisiae / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins; D012568:Schizosaccharomyces / Q000235:genetics*; D029702:Schizosaccharomyces pombe Proteins; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity
chemical_list: D002352:Carrier Proteins; D027682:Cation Transport Proteins; D018076:DNA, Complementary; D005656:Fungal Proteins; D008565:Membrane Proteins; D029701:Saccharomyces cerevisiae Proteins; D029702:Schizosaccharomyces pombe Proteins; C085258:TRK2 protein, S cerevisiae; C108462:trk1 protein, S pombe; C068664:TRK1 protein, S cerevisiae; D011188:Potassium