Eukaryote polypeptide chain-initiation factor eIF4G forms complexes with the mRNA cap-binding protein eIF4E and the ATP-dependent RNA helicase eIF4A, which constitute the initiation factor eIF4F complex. eIF4G plays an important role in the mechanism of translation by tethering between other components of the ribosomal initiation factors. Two forms of eIF4G have been reported as 2 different gene products, eIF4G1 and eIF4G2. eIF4G2 was identified as a functional homologue of eIF4G1. The homology of eIF4G2 to eIF4G1 is particularly high in central and carboxyl portions, which correspond to the eIF4A- and eIF3-binding region. The proteolysis of both eIF4G1 and eIF4G2 is associated with a decrease in cell viability and the inhibition of protein synthesis.