Glycogen synthase phosphatase interacts with heat shock factor to activateCUP1 gene transcription in Saccharomyces cerevisiae

Upon heat shock, transcription of many stress-inducible genes is rapidly an d dramatically stimulated by heat shock factor (HSF). A central region of t he yeast HSF (designated HSFrr for "repression region") was previously iden tified and proposed to be involved in repressing the activation domain unde r non-heat-shock conditions. Here, we used the phage display system to isol ate proteins that interact with HSFrr. This should identify factors that mo dulate HSF activity or directly participate in HSF-mediated transcriptional activation. We constructed a randomly sheared yeast genomic library to exp ress yeast proteins on the surface of lambda phage. HSFrr binding phages we re selected by cycles of affinity chromatography. DNA sequencing identified an HSFrr-interacting phage that contains the GAC1 gene. The GAC1 gene enco des the regulatory subunit for a type 1 serine/threonine phosphoprotein pho sphatase, Glc7. Both gac1 and glc7 mutations had little effect on HSF activ ation of gene transcription of two heat shock genes, SSA I and HSP82. In co ntrast, heat shock induction of CUP1 gene expression was completely abolish ed in a glc7 mutant and reduced in a gac1 mutant. The results demonstrate t hat the Glc7 phosphatase and its Gac1 regulatory subunit play positive role s in HSE activation of CUP1 transcription.