Redox regulation of AMP synthesis in yeast: a role of the Bas1p and Bas2p transcription factors

Expression of yeast AMP synthesis genes (ADE genes) was severely affected w hen cells were grown under oxidative stress conditions. To get an insight i nto the molecular mechanisms of this new transcriptional regulation, the ro le of the Bas1p and Bas2p transcription factors, known to activate expressi on of the ADE genes, was investigated. In vitro, DNA-binding of Bas1p was s ensitive to oxidation. However, this sensitivity could not account for the regulation of the ADE genes because we showed, using a BAS1-VP16 chimera, t hat Bas1p DNA-binding activity was not sensitive to oxidation in vivo. Cons istently, a triple cysteine mutant of Bas1p (fully resistant to oxidation i n vitro) was unable to restore transcription of the ADE genes under oxidati ve conditions. We then investigated the possibility that Bas2p could be the oxidative stress responsive factor. Interestingly, transcription of the PH O5 gene, which is dependent on Bas2p but not on Bas1p, was found to be seve rely impaired by oxidative stress. Nevertheless, a Bas2p cysteine-free muta nt was not sufficient to confer resistance to oxidative stress. Finally, we found that a Bas1p-Bas2p fusion protein restored ADE gene expression under oxidative conditions, thus suggesting that redox sensitivity of ADE gene e xpression could be due to an impairment of Bas1p/Bas2p interaction. This hy pothesis was further substantiated in a two hybrid experiment showing that Bas1p/Bas2p interaction is affected by oxidative stress.