THE ROLE OF THE YAP1 AND YAP2 GENES IN THE REGULATION OF THE ADAPTIVEOXIDATIVE STRESS RESPONSES OF SACCHAROMYCES-CEREVISIAE

The YAP1 and YAP2 genes encode yeast transcription factors of the c-ju n family. We show that yeast mutants deleted for either the YAP1 or th e YAP2 genes are hypersensitive to oxidants, particularly H2O2, and th at these genes play a role in regulating the induction of the H2O2 ada ptive stress response in Saccharomyces cerevisiae. They do not signifi cantly affect the regulation of the superoxide adaptive stress respons e. The intrinsic resistance of stationary-phase and respiring yeast ce lls towards superoxide anions is unaffected by deletion of the YAP1 an d YAP2 genes. However, resistance towards H2O2 under these conditions is significantly reduced. We show that expression of the yeast GSH1 ge ne (encoding gamma-glutamylcysteine synthetase) and the SSA1 gene (enc oding an HSP70 isoform) are induced by oxidants. Unlike the SSA1 and t hioredoxin (TRX2) genes, expression of the GSH1 gene is more strongly induced by superoxide anions than by H2O2 In the absence of added oxid ants, transcription of the GSH1 gene is reduced in strains carrying th e yap1 deletion. However, we show that Yap1 is not required for the su peroxide anion-mediated induction of GSH1 gene expression. Furthermore , white the H2O2-mediated induction of SSA1 expression is shown to be YAP1 dependent, the heat-shock-mediated induction of the SSA1 gene doe s not require YAP1. We also present evidence to show that the YAP2 gen e does not regulate the expression of the TRX2, SSA1 or GSH1 genes.