ELEVATED EXPRESSION OF STRESS-RESPONSE GENES RESULTING FROM DELETION OF THE PHO85 GENE

The cyclin-dependent protein kinase Pho85 is a known negative regulato ry factor for two stress response genes, PHO5 and GSY2, which encode t he inducible form of acid phosphatase and glycogen synthase, respectiv ely, in the yeast Saccharomyces cerevisiae. Cells carrying a disruptio n of the PHO85 gene inappropriately express both PHO5 and GSY2, result ing in the increase in phosphate scavenging and hyperaccumulation of g lycogen in nutrient-rich conditions, Constitutive activation of PKA in a pho85 mutant suppresses the hyperaccumulation of glycogen, This wor k presents data to show that, at least in part, the suppression of gly cogen biosynthesis upon activation of PKA in a pho85 mutant results fr om the suppression of GSY2 expression. In addition to GSY2, disruption of the PHO85 gene inappropriately triggers the derepression of two ot her stress response genes, HSP12 and UB14. At least in the case of GSY 2, regulation of transcription by Pho85 is not through the stress-resp onsive cis-promoter elements (STRE). Furthermore, Pho85 may associate with the known cyclin Pho80 in the transcriptional regulation of these genes.