CHARACTERIZATION OF A 2ND GENE (ZSOD22) OF NA+ H+ ANTIPORTER FROM SALT-TOLERANT YEAST ZYGOSACCHAROMYCES-ROUXII AND FUNCTIONAL EXPRESSION OFZSOD2 AND ZSOD22 IN SACCHAROMYCES-CEREVISIAE/

We reported in our previous paper on the characterization of the Na+/H +-antiporter gene (ZSOD2) closely related to the salt-tolerance of yea st Zygosaccharomyces rouxii. In the present paper, we have cloned a se cond gene (ZSOD22) of Na+/H+ antiporter from Z. rouxii. The deduced am ino acid sequence of Zsod22p was highly homologous to that of Zsod2p, Sod2p from Schizosaccharomyces pombe, and Nha1p from Saccharomyces cer evisiae. The open reading frames (ORFs) from ZSOD2 or ZSOD22 were inse rted into a yeast expression vector pYES2, and their constructs (pZSOD 2 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 ZSOD 22 did not show any phenotypes related to salt tolerance or osmotolera nce, unlike that of ZSOD2. The transcriptional expression of ZSOD22 wa s not observed by Northern blot analysis even in Z. rouxii cells subje cted to NaCl-shock. From these results we conclude that although Z. ro uxii 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 sequenc e databases with the following accession number: AB010106. (C) 1998 Jo hn Wiley & Sons. Ltd.