Journal of Biological Chemistry
Volume 275, Issue 47, 24 November 2000, Pages 37011-37020
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MECHANISMS OF SIGNAL TRANSDUCTION
HEAT Repeats Mediate Plasma Membrane Localization of Tor2p in Yeast*

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The subcellular distribution of Tor1p and Tor2p, two phosphatidylinositol kinase homologs and targets of the immunosuppressive drug rapamycin in Saccharomyces cerevisiae, was analyzed. We found that Tor protein is peripherally associated with membranes. Subcellular fractionation and immunofluorescence studies showed that Tor1p and Tor2p associate with the plasma membrane and a second fraction that is distinct from Golgi, vacuoles, mitochondria, and nucleus and may represent vesicular structures. Pulse-chase experiments showed that association of Tor protein with plasma membrane and the second compartment is fast, does not appear to involve components of endocytic, secretory, or Golgi to vacuole transport pathways, and is not affected by the immunosuppressive drug rapamycin. Deletion analysis reveals that two domains within Tor2p independently mediate localization to both compartments. These domains are composed of HEAT repeats that are thought to act as protein-protein interaction surfaces. Our studies therefore place Tor proteins at the site of action of their known downstream effectors and suggest that they may be part of a multiprotein complex.

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Published, JBC Papers in Press, September 5, 2000, DOI 10.1074/jbc.M007296200

*

This work was supported by grants from the Swiss National Science Foundation and the Canton of Basel (to M. N. H.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Present address: Dept. of Pharmacology, University of Wisconsin Medical School, 1300 University Ave., Madison, WI 53706.