LST8, a Saccharomyces cerevisiae gene encoding a 34-kD WD-repeat protein, was identified by mutations that caused defects in sorting Gap1p to the plasma membrane. Here, we report that the Gap1p sorting defect in the lst8-1 mutant results from derepression of Rtg1/3p activity and the subsequent accumulation of high levels of intracellular amino acids, which signal Gap1p sorting to the vacuole. To identify the essential function of Lst8p, we isolated lst8 mutants that are temperature-sensitive for growth. These mutants show hypersensitivity to rapamycin and derepressed Gln3p activity like cells with compromised TOR pathway activity. Like tor2 mutants, lst8 mutants also have cell wall integrity defects. Confirming a role for Lst8p in the TOR pathway, we find that Lst8p associates with both Tor1p and Tor2p and is a peripheral membrane protein that localizes to endosomal or Golgi membranes and cofractionates with Tor1p. Further, we show that a sublethal concentration of rapamycin mimics the Gap1p sorting defect of an lst8 mutant. Finally, the different effects of lst8 alleles on the activation of either the Rtg1/3p or Gln3p transcription factors reveal that these two pathways constitute distinct, genetically separable outputs of the Tor–Lst8 regulatory complex.
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28 April 2003
Article|
April 28 2003
LST8 negatively regulates amino acid biosynthesis as a component of the TOR pathway
Esther J. Chen,
Esther J. Chen
Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139
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Chris A. Kaiser
Chris A. Kaiser
Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139
Search for other works by this author on:
Esther J. Chen
Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139
Chris A. Kaiser
Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139
Address correspondence to Chris A. Kaiser 68-533, Dept. of Biology, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139. Tel.: (617) 253-9804. Fax: (617) 253-6622. E-mail: [email protected]
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Abbreviation used in this paper: YPD, yeast extract/peptone/dextrose.
Received:
October 25 2002
Revision Received:
February 24 2003
Accepted:
February 24 2003
Online ISSN: 1540-8140
Print ISSN: 0021-9525
The Rockefeller University Press
2003
J Cell Biol (2003) 161 (2): 333–347.
Article history
Received:
October 25 2002
Revision Received:
February 24 2003
Accepted:
February 24 2003
Citation
Esther J. Chen, Chris A. Kaiser; LST8 negatively regulates amino acid biosynthesis as a component of the TOR pathway . J Cell Biol 28 April 2003; 161 (2): 333–347. doi: https://doi.org/10.1083/jcb.200210141
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