Identification of Residues That Underpin Interactions within the Eukaryotic Initiation Factor (eIF2) 2B Complex

Eukaryotic initiation factor 2B (eIF2B) plays a key role in protein synthesis and in its control. It comprises five different subunits, alpha-epsilon, of which eIF2B epsilon contains the catalytic domain. Formation of the complete complex is crucial for full activity and proper control of eIF2B. Mutations in the genes for eIF2B cause an often severe neurological disorder, vanishing white matter. eIF2B gamma and eIF2B epsilon contain homologous and conserved domains with sequence similarity to nucleotidyl transferases (NTs) and acyl transferases and can form a binary complex. The latter contain a hexad repeat that mainly comprises isoleucyl residues (hence termed the I-patch region). These data reveal that certain residues in the NT domains of eIF2B gamma/epsilon, which are highly conserved throughout eukaryotes, play key roles in the interactions between subunits in the eIF2B complex. Our data show that the I-patch regions are important in the interactions between the catalytic eIF2B gamma epsilon complex and the other subunits. We also studied the functional effects of vanishing white matter mutations in the NT and I-patch domains. Lastly, our data show that eIF2B gamma promotes the expression of eIF2B epsilon, providing a mechanism for achieving correct stoichiometry of these eIF2B subunits in the cell.