Translation Initiation Factor eIF4G‐1 Binds to eIF3 Through the eIF3e Subunit

Abstract

The interactions of mammalian eIF4G with several ligands involved in initiation of translation, including eIF4E, eIF4A, PABP, and Mnk, have been mapped to distinct domains on both eIF4G and the ligand. Interaction of eIF4G with eIF3 is one of the most critical steps during translation initiation since it is required for mRNA binding to the 40S ribosomal subunit. In this study we sought the subunit(s) of human eIF3 that mediate its interaction with human eIF4G-1. Various subunits were implicated using several standard methods for detecting protein-protein interactions, but only eIF3e (p48/Int-6) scored in every assay. Recombinant eIF3e specifically inhibited cap-dependent translation but not eIF4G-independent translation. Furthermore, addition of eIF3e caused a shift of capped mRNA from heavy to light polysomes, indicating a defect in translation initiation. Finally, addition of purified recombinant full-length eIF4G-1f was able to restore cap-dependent translation that had been inhibited by the presence of eIF3e. Together, these data support the notion that eIF3e is involved in direct interaction of human eIF3 with human eIF4G-1 and formation of the 48S complex during translation initiation, though a complete mechanism of inhibition by eIF3e has not yet been explicitly tested. (Supported by Grant # GM20818 and GM22135 from the NIH.)