The Saccharomyces cerevisiae Sko1p transcription factor mediates HOG pathway-dependent osmotic regulation of a set of genes encoding enzymes implicated in protection from oxidative damage

A major part of the transcriptional response of yeast cells to osmotic shoc k is controlled by the HOG pathway and several downstream transcription fac tors. Sko1p is a repressor that mediates HOG pathway-dependent regulation b y binding to CRE sites in target promoters. Here, we report five target gen es of Hog1p-Sko1p: GRE2, AHP1, SFA1, GLR1 and YML131w. The two CREs in the GRE2 promoter function as activating sequences and, hence, bind (an) activa tor protein(s). However, the two other yeast CRE-binding proteins, Aca1p an d Aca2p, are not involved in regulation of the GRE2 promoter under osmotic stress. In the absence of the co-repressor complex Tup1p-Ssn6p/Cyc8p, which is recruited by Sko1p, stimulation by osmotic stress is still observed. Th ese data indicate that Sko1p is not only required for repression, but also involved in induction upon osmotic shock. All five Sko1p targets encode oxi doreductases with demonstrated or predicted roles in repair of oxidative da mage. Altered basal expression levels of these genes in hog1 Delta and sko1 Delta mutants may explain the oxidative stress phenotypes of these mutants . All five Sko1p target genes are induced by oxidative stress, and inductio n involves Yap1p. Although Sko1p and Yap1p appear to mediate osmotic and ox idative stress responses independently, Sko1p may affect Yap1p promoter acc ess or activity. The five Sko1p target genes described here are suitable mo dels for studying the interplay between osmotic and oxidative responses at the molecular and physiological levels.