THE SACCHAROMYCES-CEREVISIAE HSP12 GENE IS ACTIVATED BY THE HIGH-OSMOLARITY GLYCEROL PATHWAY AND NEGATIVELY REGULATED BY PROTEIN-KINASE-A

The HSP12 gene encodes one of the two major small heat shock proteins of Saccharomyces cerevisiae. Hsp12 accumulates massively in yeast cell s exposed to heat shock, osmostress, oxidative stress, and high concen trations of alcohol as well as in early-stationary-phase cells. We hav e cloned an extended 5'-flanking region of the HSP12 gene in order to identify cia-acting elements involved in regulation of this highly exp ressed stress gene. A detailed analysis of the HSP12 promoter region r evealed that five repeats of the stress-responsive CCCCT motif (stress -responsive element [STRE]) are essential to confer, wild-type induced levels on a reporter gene upon osmostress, heat shock, and entry into stationary phase. Disruption of the HOG1 and PBS2 genes leads to a dr amatic decrease of the HSP12 inducibility in osmostressed cells, where as overproduction of Hog1 produces a fivefold increase in wild-type in duced levels upon a shift to a high salt concentration. On the other h and, mutations resulting in high protein kinase A (PKA) activity reduc e or abolish the accumulation of the HSP12 mRNA in stressed cells. Con versely, mutants containing defective PKA catalytic subunits exhibit h igh basal levels of HSP12 mRNA. Taken together, these results suggest that HSP12 is a target of the high-osmolarity glycerol (HOG) response pathway under negative control of the Ras-PKA pathway. Furthermore, th ey confirm earlier observations that STRE-like sequences are responsiv e to a broad range of stresses and that the HOG and Ras-PKA pathways h ave antagonistic effects upon CCCCT-driven transcription.