Yap1p activates gene transcription in an oxidant-specific fashion

Positive regulation of gene expression by the yeast Saccharomyces cerevisia e transcription factor Yap1p is required for normal tolerance of oxidative stress elicited by the redox-active agents diamide and H2O2. Several groups have provided evidence that a cluster of cysteine residues in the extreme C terminus of the factor are required for normal modulation of Yap1p by oxi dant challenge. Deletion of this C-terminal cysteine-rich domain (c-CRD) pr oduces a protein that is highly active under both stressed and nonstressed conditions and is constitutively located in the nucleus. We have found that a variety of different c-CRD mutant proteins are hyperactive in terms of t heir ability to confer diamide tolerance to cells but fail to provide even normal levels of H2O2 resistance. Although the c-CRD mutant forms of Yap1p activate an artificial Yap1p responsive gene to the same high level in the presence of either diamide or H2O2, these mutant factors confer hyperresist ance to diamide but hypersensitivity to H2O2. To address this discrepancy, we have examined the ability of c-CRD mutant forms of Yap1p to activate exp ression of an authentic target gene required for H2O2 tolerance, TRX2. When assayed in the presence of c-CRD mutant forms of Yap1p, a TRX2-lacZ fusion gene fails to induce in response to H2O2. We have also identified a second cysteine-rich domain, in the N terminus (n-CRD), that is required for H2O2 but not diamide resistance and influences the localization of the protein. These data are consistent with the idea that the function of Yap1p is diff erent at promoters of loci involved in H2O2 tolerance from promoters of gen es involved in diamide resistance.