title: Phosphorylation of initiation factor eIF2 in response to stress conditions is mediated by acidic ribosomal P1/P2 proteins in Saccharomyces cerevisiae.
abstract: Eukaryotic cells contain an unusually large cytoplasmic pool of P1/P2 phosphoproteins, which form the highly flexible 60S subunit stalk that is required to interact with and activate soluble translation factors. In cells, cytoplasmic P1/P2 proteins are exchanged for ribosome-bound proteins in a process that can modulate ribosome function and translation. Here, we analysed different S. cerevisiae stalk mutants grown under stress conditions that result in eIF2α phosphorylation. These mutants either lack a cytoplasmic pool of stalk proteins or contain free but not ribosome-bound proteins. Only cells that contain free P1/P2 proteins induce eIF2 phosphorylation in vivo in response to glucose starvation or osmotic stress. Moreover, we show that free S. cerevisiae P1/P2 proteins can induce in vitro phosphorylation of the initiation factor eIF2 by stimulating the autophosphorylation and activation of GCN2 kinase. Indeed, these ribosomal proteins do not stimulate other eIF2α kinases, such as PKR and HRI. P1/P2 and the known GCN2 activator deacylated tRNA compete for stimulating the eIF2α kinase activity of GCN2, although the P1/P2 proteins are considerably more active. These findings reveal a capacity of free cytoplasmic ribosomal stalk components to stimulate eIF2α phosphorylation, which in turn would modulate translation in response to specific forms of stress that may be linked with the previously described regulatory function of the ribosomal stalk.
authors.affiliation: Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas and Universidad Autónoma de Madrid (CSIC-UAM), Madrid, Spain.
authors.forename: Antonio
authors.initials: A
authors.lastname: Jiménez-Díaz
authors.affiliation: Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas and Universidad Autónoma de Madrid (CSIC-UAM), Madrid, Spain.
authors.forename: Miguel
authors.initials: M
authors.lastname: Remacha
authors.affiliation: Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas and Universidad Autónoma de Madrid (CSIC-UAM), Madrid, Spain.
authors.forename: Juan P G
authors.initials: JP
authors.lastname: Ballesta
authors.affiliation: Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas and Universidad Autónoma de Madrid (CSIC-UAM), Madrid, Spain.
authors.forename: Juan José
authors.initials: JJ
authors.lastname: Berlanga
mesh_terms: D002458:Cell Fractionation; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D012269:Ribosomal Proteins / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D013045:Species Specificity; D013312:Stress, Physiological / Q000502:physiology*
chemical_list: D015852:Eukaryotic Initiation Factor-2; D012269:Ribosomal Proteins; D029701:Saccharomyces cerevisiae Proteins; C512912:GCN2 protein, S cerevisiae; D017346:Protein Serine-Threonine Kinases