Expression data from Saccharomyces cerevisiae WT, WT(hsf1), hac1∆ and hac1∆(hsf1)

In the yeast Saccharomyces cerevisiae, accumulation of misfolded proteins in the endoplasmic reticulum (ER) causes ER stress and activates the unfolded protein response (UPR) mediated by Hac1p, whereas the heat shock response (HSR) mediated by Hsf1p mainly regulates cytosolic processes and protects the cell from different stresses. In this study, we find that a constitutive activation of the HSR by over-expression of a mutant HSF1 gene could relieve ER stress in both wild type and hac1∆ UPR-deficient cells. We studied the genome-wide transcriptional response in order to identify regulatory mechanisms that govern the interplay between UPR and HSR responses. Interestingly, we find that the regulation of ER stress via HSR is mainly through facilitation of protein folding and secretion and not via the induction of Rpn4-dependent proteasomal activity. Four Saccharomyces cerevisiae strains, WT, WT(hsf1), hac1∆ and hac1∆(hsf1), were grown in SD-URA medium and treated with 2.5 mM DTT. After two hours induction, samples were taken for RNA extraction and hybridization on Affymetrix microarrays. Biological triplicates were applied.