In vivo analysis of the Hsp90 cochaperone Sti1 (p60).
Hsp90 interacts with Sti1 (p60) in lysates of yeast and vertebrate cells. Here we provide the first analysis of their interaction in vivo. Saccharomyces cerevisiae mutations that eliminate Sti1 or reduce intracellular concentrations of Hsp90 individually have little or no effect on growth at normal temperatures. However, when combined, the mutations greatly reduce or eliminate growth. Furthermore, overexpression of Sti1 has allele-specific effects on cells carrying various hsp90ts point mutations. These genetic interactions provide strong evidence that Hsp90 and Sti1 interact in vivo and that their functions are closely allied. Indeed, deletion of STI1 reduces the in vivo activity of the Hsp90 target protein, glucocorticoid receptor (GR). Mutations in GR that eliminate interaction with Hsp90 also eliminate the effects of the sti1 deletion. Examination of GR protein complexes in the sti1 deletion mutant reveals a selective increase in the concentration of GR-Ydj1 complexes, supporting previous hypotheses that Ydj1 functions at an early step in the maturation of GR and that Sti1 acts at an intermediate step. Deletion of STI1 also reduces the in vivo activity of another, unrelated Hsp90 target protein, v-Src. Our data indicate that Sti1 is a general factor in the maturation of Hsp90 target proteins and support earlier suggestions that Hsp90 matures even very different target proteins by a similar mechanism.
Chang
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HC
Howard Hughes Medical Institute, University of Chicago, Illinois 60637, USA.
Nathan
D F
DF
Lindquist
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S
D000591:Amino Acid Isomerases / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D000081406:Peptidyl-Prolyl Isomerase F; D021983:Cyclophilins; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D005800:Genes, Fungal / Q000235:genetics; D005804:Genes, Lethal / Q000235:genetics; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D018841:HSP90 Heat-Shock Proteins / Q000235:genetics* / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000235:genetics* / Q000378:metabolism; D018832:Molecular Chaperones; D009154:Mutation; D015688:Oncogene Protein pp60(v-src) / Q000378:metabolism; D019696:Peptidylprolyl Isomerase; D010766:Phosphorylation; D017354:Point Mutation; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000378:metabolism; D011965:Receptors, Glucocorticoid / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D014443:Tyrosine / Q000378:metabolism
D002352:Carrier Proteins; D000081406:Peptidyl-Prolyl Isomerase F; D005656:Fungal Proteins; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; C074510:HSP82 protein, S cerevisiae; D018841:HSP90 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D011965:Receptors, Glucocorticoid; D029701:Saccharomyces cerevisiae Proteins; C070319:YDJ1 protein, S cerevisiae; D014443:Tyrosine; D015688:Oncogene Protein pp60(v-src); D016392:Proto-Oncogene Proteins pp60(c-src); D000591:Amino Acid Isomerases; D021983:Cyclophilins; D019696:Peptidylprolyl Isomerase