Tor kinases are in distinct membrane-associated protein complexes in Saccharomyces cerevisiae.
Tor1p and Tor2p kinases, targets of the immune-suppressive antibiotic rapamycin, are components of a highly conserved signaling network that couples nutrient availability and cell growth. To gain insight into the molecular basis underlying Tor-dependent signaling, we used cell fractionation and immunoaffinity chromatography to examine the physical environment of Tor2p. We found that the majority of Tor2p associates with a membrane-bound compartment along with at least four other proteins, Avo1p-Avo3p and Lst8p. Using immunogold electron microscopy, we observed that Tor2p, as well as Tor1p, localizes in punctate clusters to regions adjacent to the plasma membrane and within the cell interior, often in association with characteristic membranous tracks. Cell fractionation, coimmunoprecipitation, and immunogold electron microscopy experiments confirmed that Lst8 associates with both Tor2p as well as Tor1p at these membranous sites. In contrast, we find that Kog1, the yeast homologue of the mammalian Tor regulatory protein Raptor, interacts preferentially with Tor1p. These findings provide evidence for the existence of Tor signaling complexes that contain distinct as well as overlapping components. That these complexes colocalize to a membrane-bound compartment suggests an intimate relationship between membrane-mediated signaling and Tor activity.
Wedaman
Karen P
KP
Section of Molecular and Cellular Biology and Center for Genetics and Development, Division of Biological Sciences, University of California, Davis, Davis, California 95616, USA.
Reinke
Aaron
A
Anderson
Scott
S
Yates
John
J
McCaffery
J Michael
JM
Powers
Ted
T
D000818:Animals; D000935:Antifungal Agents / Q000494:pharmacology; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D018797:Cell Cycle Proteins; D002458:Cell Fractionation; D002462:Cell Membrane / Q000378:metabolism*; D003902:Detergents / Q000737:chemistry; D007150:Immunohistochemistry; D047908:Intracellular Signaling Peptides and Proteins; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D020123:Sirolimus / Q000494:pharmacology
D000935:Antifungal Agents; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D003902:Detergents; D047908:Intracellular Signaling Peptides and Proteins; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D029701:Saccharomyces cerevisiae Proteins; D020123:Sirolimus; C110280:LST8 protein, S cerevisiae; C083324:TOR1 protein, S cerevisiae; C081135:TOR2 protein, S cerevisiae