The KlTrk1 gene encodes a low affinity transporter of the K+ uptake system in the budding yeast Kluyveromyces lactis

Potassium uptake in Saccharomyces cerevisiae is mediated by at least two proteins, known as Trk1p and Trk2p. Direct involvement in cation movements has been demonstrated for Trk1p, which is the high affinity transporter. S. cerevisiae cells also show low affinity potassium uptake, perhaps mediated by Trk2p. Mutants lacking Trk1p, lose high affinity system, but when grown with moderate potassium concentrations, Trk2p seems to replace it. Mutants lacking both proteins are viable but require at least 10 mM K(+) in the medium to sustain growth. Here we report the cloning and characterization of a gene from Kluyveromyces lactis encoding a homologue of these two proteins. KlTrkp is a 1070 amino acid peptide that shows, overall, higher homology with Trk2p than with Trk1p, and its disruption gives rise to cells with deficient potassium transport and with an increased K(+) requirement for normal growth. Determination of kinetic parameters in the K. lactis wild-type and Kltrk1Delta strains, as well as in Sctrk1Delta Sctrk2Delta S. cerevisiae cells expressing KlTrk1, indicated that this is a low affinity component of a major potassium uptake system in K. lactis.