The yeast Nha1p Na(+), K(+)/H(+) antiporter has a house-keeping role in pH and cation homeostasis. It is also needed to alleviate excess Na(+) or K(+) from the cytoplasm under high external concentrations of these cations. Erv14p, a putative cargo receptor for transmembrane proteins is required for trafficking of Nha1p from the endoplasmic reticulum to the plasma membrane. Sensitivity to high Na(+) concentrations of the erv14 mutant associated to the intracellular mislocalization of Nha1p-GFP, together with a lower Na(+) efflux, indicate the involvement of this mutual association to accomplish the survival of the yeast cell upon sodium stress. This observation is supported by the protein-protein interaction between Erv14p and Nha1p detected by the mating-based Split Ubiquitin System and co-immunoprecipitation assays. Our results indicate that even though Erv14p interacts with Nha1p through the TMD, the C-terminal is important not only for the efficient delivery of Nha1p to the plasma membrane but also for its dimerization to accomplish its role in yeast salt tolerance.

Department of Membrane Transport Institute of Physiology Czech Academy of Sciences v v i Videnska 1083 Prague 4 Krc 142 20 Czech Republic

Instituto de Biotecnología Universidad Nacional Autónoma de México Apdo Postal 510 3 Cuernavaca Morelos 62250 Mexico

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