Cloning of the SAT1 gene concerned with salt tolerance of the yeast Zygosaccharomyces rouxii

A gene complementing both NaCl hypersensitivity and a defect in the regulation of the intracellular level of Na+ caused by a sat1 mutation in Zygosaccharomyces rouxii was cloned from a genomic library of Z. rouxii NRRL 2547. Disruption of the cloned gene (SAT1) resulted in a defect in NaCl tolerance, intracellular accumulation of high levels of Na+ and low levels of K+ in the cells. The sat1(-) null mutant showed normal levels of tolerance against 15% KCl and 60% glucose. These phenotypes were the same as those of the sat1 mutant. Furthermore, the sat1 mutation was not complemented by crossing with the sat1(-) null mutant. The cloned SAT1 gene was sequenced and was determined to have an open reading frame (ORF) coding for 327 amino acid residues. Northern blot analysis using the cloned gene as a probe indicated that the transcript synthesized in cells grown in the presence of 10% NaCl was about 1,100 nucleotides in size, which was large enough to encode the SAT1 gene product. SAT1 showed 53.5% similarity with the UGA43 of Saccharomyces cerevisiae, a negative regulator of genes involved in the nitrogen assimilation pathway which contains a typical zinc-finger motif for DNA binding.