Characterization of a second gene (ZSOD22) of Na+/H+ antiporter from salt-tolerant yeastZygosaccharomyces rouxii and functional expression ofZSOD2 andZSOD22 inSaccharomyces cerevisiae

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Abstract
We reported in our previous paper on the characterization of the Na+/H+‐antiporter gene (ZSOD2) closely related to the salt‐tolerance of yeast Zygosaccharomyces rouxii. In the present paper, we have cloned a second gene (ZSOD22) of Na+/H+ antiporter from Z. rouxii. The deduced amino acid sequence of Zsod22p was highly homologous to that of Zsod2p, Sod2p from Schizosaccharomyces pombe, and Nha1p from Saccharomyces cerevisiae. The open reading frames (ORFs) from ZSOD2 or ZSOD22 were inserted into a yeast expression vector pYES2, and their constructs (pZSOD2 and pZSOD22) were used to transform the salt‐sensitive S. cerevisiae. pZSOD2‐ or pZSOD22‐harboring‐recombinant S. cerevisiae cells showed increases in salt tolerance. However, the Z. rouxii disruptant of ZSOD22 did not show any phenotypes related to salt tolerance or osmotolerance, unlike that of ZSOD2. The transcriptional expression of ZSOD22 was not observed by Northern blot analysis even in Z. rouxii cells subjected to NaCl‐shock. From these results we conclude that although Z. rouxii includes at least two copies of the Na+/H+‐antiporter gene (ZSOD2 and ZSOD22), ZSOD2 encodes a functional product as an antiporter and ZSOD22 is poorly transcribed, if at all. The nucleotide sequence data of ZSOD22 will appear in the DDBJ, EMBL and GenBank nucleotide sequence databases with the following accession number: AB010106. © 1998 John Wiley & Sons, Ltd.