The yeast Hsp110 family member, SSE1, is an Hsp90 cochaperone

In eukaryotes, production of the diverse repertoire of molecular chaperones during normal growth and in response to stress is governed by the heat sho ck transcription factor HSF. The HSC82 and HSP82 genes,encoding isoforms of the, yeast Hsp90 molecular chaperone, were recently identified as targets of the HSF carboxyl-terminal activation domain (CTA), whose expression is r equired for cell cycle progression during prolonged heat stress conditions. In the present study, we have identified additional target genes of the HS F CTA, which include nearly all of the heat shock-inducible members of the Hsp90 chaperone complex, demonstrating coordinate regulation of these compo nents by HSF. Heat shock induction of SSE1, encoding a member of the Hsp110 family of heat shock proteins, was also dependent on the HSF CTA. Disrupti on of SSE1 along with STI1, encoding an established subunit of the Hsp90 ch aperone complex, resulted in a severe synthetic growth phenotype. Sse1 asso ciated with partially purified Hsp90 complexes and deletion of the SSE1 gen e rendered cells susceptible to the Hsp90 inhibitors macbecin and geldanamy cin, suggesting functional interaction between Sse1 and Hsp90. Sse1 is requ ired for function of the glucocorticoid receptor, a model substrate of the Hsp90 chaperone machinery, and Hsp90-based repression of HSF under nonstres s conditions. Taken together, these data establish Sse1 as an integral new component of the Hsp90 chaperone complex in yeast.