title: K(+) uptake systems in the yeast Hansenula polymorpha. Transcriptional and post-translational mechanisms involved in high-affinity K(+) transporter regulation.
abstract: We have identified the two main K(+) transporters in the yeast Hansenula polymorpha. So far this is the only yeast with these transporters amenable to molecular genetic analysis. Two ORF-encoding permeases with high similarity to Trk1 and Hak1 are present in the genome of this yeast. Deletion of either of these genes led to defective growth in low K(+). The K(+) and Rb(+) uptake rates showed high affinity of Hak1 for K(+), while the affinity estimated for Trk1 was two orders of magnitude lower. TRK1 was not transcriptionally regulated and HAK1 was strongly induced in response to very low K(+) and down-regulated by the presence of K(+). This process is clearly dependent on calcineurin. The use of a set of strains carrying mutations affecting intracellular protein trafficking revealed that in response to K(+), Hak1 is endocytosed and degraded in the vacuole, this depending on the ubiquitin ligase Rsp5. This is a first insight into the transcriptional and post-translational mechanisms regulating a high-affinity K(+) transporter (HAK-type transporter) that allows cells to respond and adapt to K(+) availability.
authors: Department of Biochemistry and Molecular Biology, Institute of Biomedical Technologies, Nitrogen Metabolism Group, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Canarias, Spain.
authors: Elisa
authors: E
authors: Cabrera
authors: María C
authors: MC
authors: Álvarez
authors: Yusé
authors: Y
authors: Martín
authors: José M
authors: JM
authors: Siverio
authors: José
authors: J
authors: Ramos
mesh_terms: D001692:Biological Transport; D019703:Calcineurin / Q000378:metabolism; D027682:Cation Transport Proteins / Q000235:genetics / Q000378:metabolism*; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D015966:Gene Expression Regulation, Fungal; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010843:Pichia / Q000201:enzymology / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D014158:Transcription, Genetic
chemical_list: D027682:Cation Transport Proteins; D005656:Fungal Proteins; D026901:Membrane Transport Proteins; D019703:Calcineurin; D011188:Potassium