Affiliation:
1. Department of Biochemistry, 433 Babcock Drive, University of Wisconsin – Madison, Madison, Wisconsin 53706
Abstract
J-domain protein cochaperones drive much of the functional diversity of Hsp70-based chaperone systems. Sis1 is the only essential J-domain protein of the cytosol/nucleus of Saccharomyces cerevisiae. Why it is required for cell growth is not understood, nor is how critical its role in regulation of heat shock transcription factor 1 (Hsf1). We report that single residue substitutions in Tti1, a component of the heterotrimeric TTT complex, a specialized chaperone system for phosphatidylinositol 3-kinase-related kinase (PIKK) proteins, allow growth of cells lacking Sis1. Upon depletion of Sis1, cells become hypersensitive to rapamycin, a specific inhibitor of TORC1 kinase. In addition, levels of the three essential PIKKs (Mec1, Tra1, and Tor2), as well as Tor1, decrease upon Sis1depletion. Overexpression of Tti1 allows growth, without an increase in the other subunits of the TTT complex, Tel2 and Tti2, suggesting that it can function independent of the complex. Cells lacking Sis1, with viability supported by Tti1 suppressor, substantially upregulate some, but not all, heat shock elements activated by Hsf1. Together, our results suggest that Sis1 is required as a cochaperone of Hsp70 for the folding/maintenance of PIKKs making Sis1 an essential gene, and its requirement for Hsf1 regulation is more nuanced than generally appreciated.
Publisher
American Society for Cell Biology (ASCB)
Subject
Cell Biology,Molecular Biology
Cited by
2 articles.
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