title: Cloning and characterization of two K+ transporters of Debaryomyces hansenii.
abstract: Two genes from the halotolerant yeast Debaryomyces hansenii were cloned, DhTRK1 and DhHAK1. These genes encode K(+) transporters with sequence similarities to the TRK and HAK transporters from Debaryomyces occidentalis and Candida albicans. The DhHAK1p transporter was only expressed in K(+)-starved cells, as shown by Northern blot analysis. Both DhTRK1p and DhHAK1p were expressed in a trk1Delta trk2Delta mutant of Saccharomyces cerevisiae, unable to grow at low K(+). This expression resulted in partial recovery of growth and ability to retain K(+) at low concentrations. In liquid media, 0.5 M NaCl affected growth of these S. cerevisiae transformants as it does in D. hansenii, resulting in a much less deleterious effect than in wild-type S. cerevisiae. Kinetics of Rb(+) uptake in the transformants suggest that DhTRK1p and DhHAK1p code for moderate-affinity K(+) transporters exhibiting a sigmoid response against Rb(+) concentration and presenting a deviation from classic Michaelis-Menten kinetics at low substrate concentrations. Rb(+) uptake by the DhTRK1p transporter was stimulated by millimolar concentrations of Na(+) at pH 4.5. The good performance of DhTRK1p in the presence of NaCl may be a key feature in the halotolerance of D. hansenii.
authors.affiliation: Centro de Botânica Aplicada à Agricultura, Instituto Superior de Agronomia, TU Lisbon, 1349-017 Lisboa, Portugal.
authors.forename: Catarina
authors.initials: C
authors.lastname: Prista
authors.affiliation: Centro de Botânica Aplicada à Agricultura, Instituto Superior de Agronomia, TU Lisbon, 1349-017 Lisboa, Portugal.
authors.forename: Juan Carlos
authors.initials: JC
authors.lastname: González-Hernández
authors.affiliation: Departamento Microbiología, Escuela Técnica Superior de Ingenieros Agrónomos y de Montes, E-14071 Córdoba, Spain.
authors.forename: José
authors.initials: J
authors.lastname: Ramos
authors.affiliation: Centro de Botânica Aplicada à Agricultura, Instituto Superior de Agronomia, TU Lisbon, 1349-017 Lisboa, Portugal.
authors.forename: Maria C
authors.initials: MC
authors.lastname: Loureiro-Dias
mesh_terms: D027682:Cation Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D003001:Cloning, Molecular; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D008969:Molecular Sequence Data; D011188:Potassium / Q000378:metabolism*; D012413:Rubidium / Q000378:metabolism; D004718:Saccharomycetales / Q000187:drug effects / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D017422:Sequence Analysis, DNA; D012965:Sodium Chloride / Q000494:pharmacology
chemical_list: D027682:Cation Transport Proteins; D005656:Fungal Proteins; D012965:Sodium Chloride; D012413:Rubidium; D011188:Potassium