title: Translational control by TOR and TAP42 through dephosphorylation of eIF2alpha kinase GCN2.
abstract: Yeast protein kinase GCN2 stimulates the translation of transcriptional activator GCN4 by phosphorylating eIF2alpha in response to amino acid starvation. Kinase activation requires binding of uncharged tRNA to a histidyl tRNA synthetase-related domain in GCN2. Phosphorylation of serine 577 (Ser 577) in GCN2 by another kinase in vivo inhibits GCN2 function in rich medium by reducing tRNA binding activity. We show that rapamycin stimulates eIF2alpha phosphorylation by GCN2, with attendant induction of GCN4 translation, while reducing Ser 577 phosphorylation in nonstarved cells. The alanine 577 (Ala 577) mutation in GCN2 (S577A) dampened the effects of rapamycin on eIF2alpha phosphorylation and GCN4 translation, suggesting that GCN2 activation by rapamycin involves Ser 577 dephosphorylation. Rapamycin regulates the phosphorylation of Ser 577 and eIF2alpha by inhibiting the TOR pathway. Rapamycin-induced dephosphorylation of Ser 577, eIF2alpha phosphorylation, and induction of GCN4 all involve TAP42, a regulator of type 2A-related protein phosphatases. Our results add a new dimension to the regulation of protein synthesis by TOR proteins and demonstrate cross-talk between two major pathways for nutrient control of gene expression in yeast.
authors.affiliation: Laboratory of Gene Regulation and Development, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Vera A
authors.initials: VA
authors.lastname: Cherkasova
authors.forename: Alan G
authors.initials: AG
authors.lastname: Hinnebusch
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D015966:Gene Expression Regulation, Fungal / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D014176:Protein Biosynthesis; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D020123:Sirolimus / Q000494:pharmacology; D019892:eIF-2 Kinase / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D029701:Saccharomyces cerevisiae Proteins; D020123:Sirolimus; D019892:eIF-2 Kinase; C100984:TAP42 protein, S cerevisiae; C083324:TOR1 protein, S cerevisiae; C512912:GCN2 protein, S cerevisiae