Regulation of yAP-1 nuclear localization in response to oxidative stress

The YAP1 gene of Saccharomyces cerevisiae encodes a bZIP-containing transcription factor that is essential for the normal response of cells to oxidative stress. Under stress conditions, the activity of yAP-1 is increased, leading to the induced expression of a number of target genes encoding protective enzymes or molecules. We have examined the mechanism of this activation. Upon imposition of oxidative stress, a small increase in the DNA-binding capacity of yAP-1 occurs. However, the major change is at the level of nuclear localization; upon induction the yAP-1 protein relocalizes from the cytoplasm to the nucleus. This regulated localization is mediated by a cysteine-rich domain (CRD) at the C-terminus, its removal resulting in constitutive nuclear localization and high level activity. Furthermore, the CRD of yAP-1 is sufficient to impose regulated nuclear localization of the GAL4 DNA-binding domain. Amino acid substitutions indicated that three conserved cysteine residues in the CRD are essential for the regulation. We suggest therefore, that these cysteine residues are important in sensing the redox state of the cell and hence regulating yAP-1 activity.