title: Snf1 promotes phosphorylation of the alpha subunit of eukaryotic translation initiation factor 2 by activating Gcn2 and inhibiting phosphatases Glc7 and Sit4.
abstract: Snf1 is the ortholog of mammalian AMP-activated kinase and is responsible for activation of glucose-repressed genes at low glucose levels in budding yeast. We show that Snf1 promotes the formation of phosphorylated alpha subunit of eukaryotic translation initiation factor 2 (eIF2alpha-P), a regulator of general and gene-specific translation, by stimulating the function of eIF2alpha kinase Gcn2 during histidine starvation of glucose-grown cells. Thus, eliminating Snf1 or mutating its activation loop lowers Gcn2 kinase activity, reducing the autophosphorylation of Thr-882 in the Gcn2 activation loop, and decreases eIF2alpha-P levels in starved cells. Consistently, eliminating Reg1, a negative regulator of Snf1, provokes Snf1-dependent hyperphosphorylation of both Thr-882 and eIF2alpha. Interestingly, Snf1 also promotes eIF2alpha phosphorylation in the nonpreferred carbon source galactose, but this occurs by inhibition of protein phosphatase 1alpha (PP1alpha; Glc7) and the PP2A-like enzyme Sit4, rather than activation of Gcn2. Both Glc7 and Sit4 physically interact with eIF2alpha in cell extracts, supporting their direct roles as eIF2alpha phosphatases. Our results show that Snf1 modulates the level of eIF2alpha phosphorylation by different mechanisms, depending on the kind of nutrient deprivation existing in cells.
authors.affiliation: Laboratory of Gene Regulation and Development, Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, Bethesda, Maryland 20892, USA.
authors.forename: Vera
authors.initials: V
authors.lastname: Cherkasova
authors.forename: Hongfang
authors.initials: H
authors.lastname: Qiu
authors.forename: Alan G
authors.initials: AG
authors.lastname: Hinnebusch
mesh_terms: D003470:Culture Media / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism*; D005690:Galactose / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology; D006639:Histidine / Q000172:deficiency / Q000494:pharmacology; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D010766:Phosphorylation / Q000187:drug effects; D011485:Protein Binding / Q000187:drug effects; D054645:Protein Phosphatase 1 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D054648:Protein Phosphatase 2 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D021122:Protein Subunits / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000201:enzymology*; D029701:Saccharomyces cerevisiae Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism*
chemical_list: D003470:Culture Media; D015852:Eukaryotic Initiation Factor-2; D021122:Protein Subunits; D029701:Saccharomyces cerevisiae Proteins; D006639:Histidine; C071570:SNF1-related protein kinases; C512912:GCN2 protein, S cerevisiae; D017346:Protein Serine-Threonine Kinases; C092048:GLC7 protein, S cerevisiae; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2; C104343:SIT4 protein, S cerevisiae; D005947:Glucose; D005690:Galactose
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