title: Physical association of eukaryotic initiation factor (eIF) 5 carboxyl-terminal domain with the lysine-rich eIF2beta segment strongly enhances its binding to eIF3.
abstract: The carboxyl-terminal domain (CTD) of eukaryotic initiation factor (eIF) 5 interacts with eIF1, eIF2beta, and eIF3c, thereby mediating formation of the multifactor complex (MFC), an important intermediate for the 43 S preinitiation complex assembly. Here we demonstrate in vitro formation of a nearly stoichiometric quaternary complex containing eIF1 and the minimal segments of eIF2beta, eIF3c, and eIF5. In vivo, overexpression of eIF2 and tRNA(Met)(i) suppresses the temperature-sensitive phenotype of tif5-7A altering eIF5-CTD by increasing interaction of the mutant eIF5 with eIF2 by mass action and restoring its defective interaction with eIF3. By contrast, overexpression of eIF1 exacerbated the tif5-7A phenotype because eIF1 forms unusual inhibitory complexes with a hyperstoichiometric amount of eIF1. Formation of such complexes leads to increased GCN4 translation, independent of eIF2 phosphorylation (general control derepressed or Gcd(-) phenotype). We also provide biochemical evidence indicating that the association of eIF5-CTD with eIF2beta strongly enhances its binding to eIF3c. Our results suggest strongly that MFC formation is an ordered event involving specific enhancement of eIF5-CTD binding to eIF3 on its binding to eIF2beta. We propose that the primary function of eIF5-CTD is to serve as an assembly guide by rapidly promoting stoichiometric MFC assembly with the aid of eIF2 while excluding formation of nonfunctional complexes.
authors.affiliation: Molecular Cellular and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, Kansas 66506, USA.
authors.forename: Chingakham Ranjit
authors.initials: CR
authors.lastname: Singh
authors.forename: Yasufumi
authors.initials: Y
authors.lastname: Yamamoto
authors.forename: Katsura
authors.initials: K
authors.lastname: Asano
mesh_terms: D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism*; D039621:Eukaryotic Initiation Factor-3 / Q000378:metabolism*; D040061:Eukaryotic Initiation Factor-5 / Q000235:genetics / Q000378:metabolism*; D008239:Lysine / Q000378:metabolism; D009154:Mutation; D011233:Precipitin Tests; D011485:Protein Binding; D014176:Protein Biosynthesis / Q000502:physiology; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae
chemical_list: D015852:Eukaryotic Initiation Factor-2; D039621:Eukaryotic Initiation Factor-3; D040061:Eukaryotic Initiation Factor-5; D008239:Lysine