Activation of an Essential Calcium Signaling Pathway in Saccharomyces cerevisiae by Kch1 and Kch2, Putative Low-Affinity Potassium Transporters

Abstract

ABSTRACTIn the budding yeastSaccharomyces cerevisiae, mating pheromones activate a high-affinity Ca2+influx system (HACS) that activates calcineurin and is essential for cell survival. Here we identify extracellular K+and a homologous pair of transmembrane proteins, Kch1 and Kch2 (Prm6), as necessary components of the HACS activation mechanism. Expression of Kch1 and especially Kch2 was strongly induced during the response to mating pheromones. When forcibly overexpressed, Kch1 and Kch2 localized to the plasma membrane and activated HACS in a fashion that depended on extracellular K+but not pheromones. They also promoted growth oftrk1 trk2mutant cells in low K+environments, suggesting they promote K+uptake. Voltage-clamp recordings of protoplasts revealed diminished inward K+currents inkch1 kch2double-mutant cells relative to the wild type. Conversely, heterologous expression of Kch1 in HEK293T cells caused the appearance of inwardly rectifying K+currents. Collectively, these findings suggest that Kch1 and Kch2 directly promote K+influx and that HACS may electrochemically respond to K+influx in much the same way as the homologous voltage-gated Ca2+channels in most animal cell types.