The carboxyl-terminal domain (CTD) of eukaryotic initiation factor (eIF) 5 interacts with eIF1, eIF2β, 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 eIF2β, eIF3c, and eIF5. In vivo, overexpression of eIF2 and tRNA iMet 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 eIF2β 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 eIF2β. 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.
All Science Journal Classification (ASJC) codes
- Molecular Biology
- Cell Biology