Cation/H + antiporters mediate potassium and sodium fluxes in Pichia sorbitophila . Cloning of the PsNHA1 and PsNHA2 genes and expression in Saccharomyces cerevisiae

Pichia sorbitophila grows rapidly in the presence of very high NaCl concentrations. Under these conditions, even when the K + concentration is low, P. sorbitophila cells can maintain low Na + and high K + contents. This remarkable capacity of P. sorbitophila fails when the external pH is not acidic. This indicates that Na + efflux is mediated by an electroneutral Na + /H + antiporter. We have cloned and sequenced two genes designated as PsNHA1 and PsNHA2 , which probably encode two antiporters of this type. The genes present high similarity with the corresponding genes from other yeasts. The heterologous expression of PsNHA1 or PsNHA2 in a Saccharomyces cerevisiae mutant lacking the Na + efflux systems and sensitive to high concentrations of Na + and K + rescued the tolerance and the ability to extrude both cations. The Accession Nos of the sequenced DNA fragments are: PsNHA1 , AJ496431; PsNHA2 , AJ496432. (TC 2.A.36) Copyright © 2002 John Wiley & Sons, Ltd.