DUAL REGULATION BY HEAT AND NUTRIENT STRESS OF THE YEAST HSP150 GENE ENCODING A SECRETORY GLYCOPROTEIN

We have cloned and characterized the HSP150 gene of Saccharomyces cerevisiae, which encodes a glycoprotein (hsp 150) that is secreted into the growth medium. Unexpectedly, the HSP150 gene was found to be regulated by heat shock and nitrogen starvation. Shifting the cells from 24-degrees-C to 37-degrees-C resulted in an abrupt increase in the steady-state level of the HSP150 mRNA, and de novo synthesized hsp150 protein. Returning the cells to 24-degrees-C caused a rapid decrease in mRNA and protein synthesis to basal levels. The HSP150 5'-flanking region contains several heat shock element-like sequences (HSE). To study the function of these sequences, a strain bearing a disrupted copy of the HSP150 gene was transformed with plasmids in which the coding region of HSP150, or a HSP150-lacZ fusion gene, was preceded by 5' deletion derivatives of the HSP150 promoter. Site-directed mutagenesis of one HSE-like element, located between the TATA box and transcription initiation sites, abolished heat activation of transcription. In addition to heat shock, the HSP150 gene is regulated by the availability of nutrients in the growth medium. The HSP150 mRNA level was increased by nitrogen limitation at 24-degrees-C, even when under the control of a HSP150 promoter region of 137 bp carrying the mutagenized HSE.