Regulatory factors controlling transcription of Saccharomyces cerevisiae IXR1 by oxygen levels: a model of transcriptional adaptation from aerobiosis to hypoxia implicating ROX1 and IXR1 cross-regulation

摘要

pIxr1p from iSaccharomyces cerevisiae/i has been previously studied because it binds to DNA containing intrastrand cross-links formed by the anticancer drug cisplatin. Ixr1p is also a transcriptional regulator of anaerobic/hypoxic genes, such as iSRP1/TIR1/i, which encodes a stress-response cell wall manoprotein, and iCOX5B/i, which encodes the Vb subunit of the mitochondrial complex cytochrome ic/i oxidase. However, factors controlling iIXR1/i expression remained unexplored. In the present study we show that iIXR1/i mRNA levels are controlled by oxygen availability and increase during hypoxia. In aerobiosis, low levels of iIXR1/i expression are maintained by Rox1p repression through the general co-repressor complex Tup1–Ssn6. Ixr1p itself is necessary for full iIXR1/i expression under hypoxic conditions. Deletion analyses have identified the region in the iIXR1/i promoter responsible for this positive auto-control (nucleotides ?557 to ?376). EMSA (electrophoretic mobility-shift assay) and ChIP (chromatin immunoprecipitation) assays show that Ixr1p binds to the iIXR1/i promoter both iin vitro/i and iin vivo/i. Ixr1p is also required for hypoxic repression of iROX1/i and binds to its promoter. iUPC2/i deletion has opposite effects on iIXR1/i and iROX1/i transcription during hypoxia. Ixr1p is also necessary for resistance to oxidative stress generated by Hsub2/subOsub2/sub. iIXR1/i expression is moderately activated by Hsub2/subOsub2/sub and this induction is Yap1p-dependent. A model of iIXR1/i regulation as a relay for sensing different signals related to change in oxygen availability is proposed. In this model, transcriptional adaptation from aerobiosis to hypoxia depends on iROX1/i and iIXR1/i cross-regulation./p