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J. Biol. Chem., Vol. 278, Issue 48, 47441-47448, November 28, 2003

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The Hsp90 Molecular Chaperone Complex Regulates Maltose Induction and Stability of the Saccharomyces MAL Gene Transcription Activator Mal63p^*

Mehtap Bali, Bin Zhang¶, Kevin A. Morano||**, and Corinne A. Michels

From the Biology Department, Queens College and the Graduate School of the City University of New York, Flushing, New York 11367 and the ^||Department of Microbiology and Molecular Genetics, University of Texas-Houston Medical School, Houston, Texas 77303

Induction of the Saccharomyces MAL structural genes encoding maltose permease and maltase requires the MAL activator, a DNA-binding transcription activator. Genetic analysis of MAL activator mutations suggested that protein folding and stability play an important role in MAL activator regulation and led us to explore the role of the Hsp90 molecular chaperone complex in the regulation of the MAL activator. Strains carrying mutations in genes encoding components of the Hsp90 chaperone complex, hsc82 hsp82-T101I and hsc82 cpr7, are defective for maltase induction and exhibit significantly reduced growth rates on media containing a limiting concentration of maltose (0.05%). This growth defect is suppressed by providing maltose in excess. Using epitope-tagged alleles of the MAL63 MAL activator, we showed that Mal63p levels are drastically reduced following depletion of cellular Hsp90. Overexpression (3-fold) of Mal63p in the hsc82 hsp82-T101I and hsc82 cpr7 strains suppresses their Mal^– growth phenotype, suggesting that Mal63p levels are limiting for maltose utilization in strains with abrogated Hsp90 activity. Consistent with this, the half-life of Mal63p is significantly shorter in the hsc82 cpr7 strain (reduced about 6-fold) and modestly affected in the Hsp90-ts strain (reduced about 2-fold). Most importantly, triple hemagglutinin-tagged Mal63p protein is found in association with Hsp90 as demonstrated by co-immunoprecipitation. Taken together, these results identify the inducible MAL activator as a client protein of the Hsp90 molecular chaperone complex and point to a critical role for chaperone function in alternate carbon source utilization in Saccharomyces cerevisiae.

Received for publication, August 27, 2003

^* This work was supported by NIGMS, National Institutes of Health Grant GM28216 (to C. A. M.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

This work was done in partial fulfillment of the requirements of a Ph.D. degree from the Graduate School of the City University of New York.

^¶ This work was done in partial fulfillment of the requirements of a Master's degree from Queens College of City University of New York.

^** Supported by Research Scholar Grant MBC-103134 from the American Cancer Society.

To whom correspondence should be addressed: Biology Dept., Queens College and the Graduate School of CUNY, 65-30 Kissena Blvd., Flushing, NY 11367. Tel.: 718-997-3400; Fax: 718-997-3321; E-mail: corinne_michels{at}qc.edu.

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