PMID:11997479

Citation	Crespo, JL, Powers, T, Fowler, B and Hall, MN (2002) The TOR-controlled transcription activators GLN3, RTG1, and RTG3 are regulated in response to intracellular levels of glutamine. Proc. Natl. Acad. Sci. U.S.A. 99:6784-9
Abstract	The essential, rapamycin-sensitive TOR kinases regulate a diverse set of cell growth-related readouts in response to nutrients. Thus, the yeast TOR proteins function as nutrient sensors, in particular as sensors of nitrogen and possibly carbon. However, the nutrient metabolite(s) that acts upstream of TOR is unknown. We investigated the role of glutamine, a preferred nitrogen source and a key intermediate in yeast nitrogen metabolism, as a possible regulator of TOR. We show that the glutamine synthetase inhibitor L-methionine sulfoximine (MSX) specifically provokes glutamine depletion in yeast cells. MSX-induced glutamine starvation caused nuclear localization and activation of the TOR-inhibited transcription factors GLN3, RTG1, and RTG3, all of which mediate glutamine synthesis. The MSX-induced nuclear localization of GLN3 required the TOR-controlled, type 2A-related phosphatase SIT4. Other TOR-controlled transcription factors, GAT1/NIL1, MSN2, MSN4, and an unknown factor involved in the expression of ribosomal protein genes, were not affected by glutamine starvation. These findings suggest that the TOR pathway senses glutamine. Furthermore, as glutamine starvation affects only a subset of TOR-controlled transcription factors, TOR appears to discriminate between different nutrient conditions to elicit a response appropriate to a given condition.
Links	PubMed PMC124480 Online version:10.1073/pnas.102687599
Keywords	Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; Carrier Proteins/genetics; Cation Transport Proteins; DNA-Binding Proteins/metabolism; Enzyme Inhibitors/pharmacology; Fungal Proteins/genetics; Fungal Proteins/metabolism; Gene Expression; Glutamate-Ammonia Ligase/antagonists & inhibitors; Glutamic Acid/metabolism; Glutamine/metabolism; Intracellular Fluid/metabolism; Methionine Sulfoximine/pharmacology; Phosphatidylinositol 3-Kinases; Phosphotransferases (Alcohol Group Acceptor)/genetics; Phosphotransferases (Alcohol Group Acceptor)/metabolism; Repressor Proteins; Saccharomyces cerevisiae/drug effects; Saccharomyces cerevisiae/growth & development; Saccharomyces cerevisiae/metabolism; Saccharomyces cerevisiae Proteins; Signal Transduction; Trans-Activators/metabolism; Transcription Factors
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