Role of Hog1 and Yaf9 in the transcriptional response of Saccharomyces cerevisiae to cesium chloride.

We analyzed the global transcriptional response of Saccharomyces cerevisiae cells exposed to different concentrations of CsCl in the growth medium and at different times after addition. Early responsive genes were mainly involved in cell wall structure and biosynthesis. About half of the induced genes were previously shown to respond to other alkali metal cations in a Hog1-dependent fashion. Western blot analysis confirmed that cesium concentrations as low as 100 mM activate Hog1 phosphorylation. Another important fraction of the cesium-modulated genes requires Yaf9p for full responsiveness as shown by the transcriptome of a yaf9-deleted strain in the presence of cesium. We showed that a cell wall-restructuring process promptly occurs in response to cesium addition, which is dependent on the presence of both Hog1 and Yaf9 proteins. Moreover, the sensitivity to low concentration of cesium of the yaf9-deleted strain is not observed in a strain carrying the hog1/yaf9 double deletion. We conclude that the observed early transcriptional modulation of cell wall genes has a crucial role in S. cerevisiae adaptation to cesium.