In Saccharomyces cerevisiae, TRK1 and TRK2 genes encode partially redundant K(+) transporters. Direct involvement in K(+) uptake has been shown for Trk1p since cells growing under limiting environmental K(+) concentrations demand its presence. The biological role of Trk2p is less understood. In our experiments, TRK2 overexpression improved the ability of trk1 cells to grow in low K(+) and led to a higher accumulation of K(+). Using diS-C(3)(3) as a potentiometric probe, we revealed a higher hyperpolarization of trk2 cells compared to the wild type. In addition, the deletion of TRK2 in the trk1 genetic background increased the cell sensitivity to hygromycin B, spermine, and TMA. Our studies reinforced the conclusion that Trk1p is the prominent K(+) uptake transporter and for the first time revealed that though Trk2p is much less effective, its activity contributes significantly to K(+) supply and the maintenance of plasma-membrane potential.

Department of Membrane Transport Institute of Physiology Academy of Sciences of the Czech Republic v v i 14220 Prague 4 Czech Republic

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