title: Molecular cloning and functional expression in bacteria of the potassium transporters CnHAK1 and CnHAK2 of the seagrass Cymodocea nodosa.
abstract: The cDNAs CnHAK1 and CnHAK2, encoding K+ transporters, were amplified from the leaves of the seagrass Cymodocea nodosa. None of these transporters suppressed the K+ deficiency of a Saccharomyces cerevisiae mutant, but both suppressed the equivalent defect of an Escherichia coli mutant. Overexpression of the transporter CnHAKI, but not CnHAK2, mediated very rapid K+ or Rb+ influxes in the E. coli mutant. The concentration dependence of these influxes demonstrated that CnHAK1 is a low-affinity K+ transporter, which does not discriminate between K+ and Rb+. CnHAK1 expressed in E. coli worked in reverse when the external K+ concentrations were low, and we established the condition of a simple functional test of K+ loss for transporters of the Kup-HAK family. In comparison with its homologue barley transporter HvHAK2, CnHAKI was insensitive to Na+.
authors.affiliation: Departamento de Biotecnología, Escuela Técnica Superior de Ingenieros Agrónomos, Universidad Politécnica de Madrid, Spain.
authors.forename: Blanca
authors.initials: B
authors.lastname: Garciadeblas
authors.forename: Begoña
authors.initials: B
authors.lastname: Benito
authors.forename: Alonso
authors.initials: A
authors.lastname: Rodríguez-Navarro
mesh_terms: D000595:Amino Acid Sequence; D001692:Biological Transport / Q000187:drug effects; D027682:Cation Transport Proteins / Q000235:genetics* / Q000378:metabolism; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics*; D015870:Gene Expression; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D006109:Poaceae / Q000235:genetics*; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology; D012413:Rubidium / Q000378:metabolism; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D012964:Sodium / Q000494:pharmacology
chemical_list: D027682:Cation Transport Proteins; D018076:DNA, Complementary; C110543:HAK1 protein, plant; C110544:HAK2 protein, Hordeum vulgare; D010940:Plant Proteins; D012964:Sodium; D012413:Rubidium; D011188:Potassium