Thioredoxin deficiency causes the constitutive activation of Yap1, an AP-1-like transcription factor in Saccharomyces cerevisiae

Yap1 is a transcription factor that responds to oxidative stress in Saccharomyces cerevisiae. The activity of Yap1 is regulated at the level of its intracellular localization, and a cysteine-rich domain at the C terminus of Yap1 is involved in this regulation. We investigated the effects of redox-regulatory proteins, thioredoxin and glutaredoxin, on the regulation of Yap1, using the deficient mutants of these thiol-disulfide oxidoreductases. In the thioredoxin-deficient mutant (trx1 Delta/trx2 Delta), Yap1 was constitutively concentrated in the nucleus and the level of expression of the Yap1 target genes was high under normal conditions, while this was not the case for the glutaredoxin-deficient mutant (grx1 Delta/grx2 Delta). No distinct difference was observed in the levels of Yap1 protein between the wild type and trx1 Delta/trx2 Delta. The constitutive activation of Yap1 in trx1 Delta/trx2 Delta was observed under aerobic conditions but not under anaerobic conditions. These findings suggest that thioredoxin has negative effects on this regulation via the redox states. We also show the synthetic lethality between yap1 Delta and trx1 Delta/trx2 Delta mutation, but the yap1 Delta/grx1 Delta/grx2 Delta triple mutant was viable, suggesting a difference of the functions between thioredoxin and glutaredoxin and a genetic interaction between Yap1 and thioredoxin in vivo.