Isolation and Characterization of STI1, a Stress-Inducible Gene from Saccharomyces cerevisiae

Abstract

We have isolated a gene from the yeast Saccharomyces cerevisiae that encodes a 2.0-kilobase heat-inducible mRNA. This gene, which we have designated STI1, for stress inducible, was also induced by the amino acid analog canavanine and showed a slight increase in expression as cells moved into stationary phase. The STI1 gene encodes a 66-kilodalton protein, as determined from the sequence of the longest open reading frame. The putative STI1 protein, as identified by two-dimensional gel electrophoresis, migrated in the region of 73 to 75 kilodaltons as a series of four isoforms with different isoelectric points. STI1 is not homologous to the other conserved HSP70 family members in yeasts, despite similarities in size and regulation. Cells carrying a disruption mutation of the STI1 gene grew normally at 30°C but showed impaired growth at higher and lower temperatures. Overexpression of the 5777 gene resulted in substantial trans-activation of SSA4 promoter-reporter gene fusions, indicating that STI1 may play a role in mediating the heat shock response of some HSP70 genes.