BACKGROUND: In yeast, 14-3-3 proteins bind to hundreds of phosphorylated proteins and play a role in the regulation of many processes including tolerance to NaCl. However, the mechanism of 14-3-3 involvement in the cell answer to salt or osmotic stresses is weakly understood. METHODS: We studied the role of the Saccharomyces cerevisiae 14-3-3 homologs Bmh1 and Bmh2 in the regulation of alkali-metal-cation homeostasis using the genetic-interaction approach. Obtained results were confirmed with the Bimolecular-Fluorescence-Complementation method. RESULTS: Deletion of BMH1, encoding the major 14-3-3 isoform, resulted in an increased sensitivity to Na+, Li+ and K+ and to cationic drugs but did not affect membrane potential. This bmh1Δ phenotype was complemented by overexpression of BMH2. Testing the genetic interaction between BMH genes and genes encoding plasma-membrane cation transporters revealed, that 14-3-3 proteins neither interact with the potassium uptake systems, nor with the potassium-specific channel nor with the Na+(K+)-ATPases. Instead, a genetic interaction was identified between BMH1 and NHA1 which encodes an Na+(K+)/H+ antiporter. In addition, a physical interaction between 14-3-3 proteins and the Nha1 antiporter was shown. This interaction does not depend on the phosphorylation of the Nha1 antiporter by Hog1 kinase. Our results uncovered a previously unknown interaction partner of yeast 14-3-3 proteins and provided evidence for the previously hypothesized involvement of Bmh proteins in yeast salt tolerance. GENERAL SIGNIFICANCE: Our results showed for the first time that the yeast 14-3-3 proteins and an alkali-metal-cation efflux system interact and that this interaction enhances the cell survival upon salt stress.
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