The eukaryotic initiation factor (eIF) 5 HEAT domain mediates multifactor assembly and scanning with distinct interfaces to eIF1, eIF2, eIF3, and eIF4G

Eukaryotic translation initiation factor (eIF) 5 is crucial for the assembly of the eukaryotic preinitiation complex. This activity is mediated by the ability of its C-terminal HEAT domain to interact with elF1, elF2, and elF3 in the multifactor complex and with elF4G in the 48S complex. However, the binding sites for these factors on elF5-C-terminal domain (CTD) have not been known. Here we present a homology model for elF5-CTD based on the HEAT domain of elF2BE. We show that the binding site for elf2 beta is located in a surface area containing aromatic and acidic residues (aromatic/ acidic boxes), that the binding sites for elF1 and elF3c are located in a conserved surface region of basic residues, and that elF4G binds elF5-CTD at an interface overlapping with the acidic area. Mutations in these distinct elF5 surface areas impair GCN4 translational control by disrupting preinitiation complex interactions. These results indicate that the elF5 HEAT domain is a critical nucleation core for preinitiation complex assembly and function.