The Translation Initiation Factor eIF-4E Binds to a Common Motif Shared by the Translation Factor eIF-4γ and the Translational Repressors 4E-Binding Proteins

TLDR

eIF‑4E is a cap‑binding component of the eIF‑4F complex, the least abundant initiation factor and a target of growth‑regulatory pathways, and its interaction with newly identified 4E‑binding proteins is negatively regulated by phosphorylation in response to insulin or growth factors. The study aimed to characterize the molecular interactions between eIF‑4E and the other subunits of eIF‑4F and with the 4E‑binding proteins. A 49‑amino‑acid region of eIF‑4γ, containing a conserved 12‑amino‑acid motif shared with 4E‑binding proteins, was identified as essential for binding to eIF‑4E. Mutations in this motif disrupted eIF‑4E binding, demonstrating its essential role in eIF‑4F assembly and in insulin‑ and growth‑factor‑mediated translational regulation.

Abstract

Eukaryotic translation initiation factor 4E (eIF-4E), which possesses cap-binding activity, functions in the recruitment of mRNA to polysomes as part of a three-subunit complex, eIF-4F (cap-binding complex). eIF-4E is the least abundant of all translation initiation factors and a target of growth regulatory pathways. Recently, two human cDNAs encoding novel eIF-4E-binding proteins (4E-BPs) which function as repressors of cap-dependent translation have been cloned. Their interaction with eIF-4E is negatively regulated by phosphorylation in response to cell treatment with insulin or growth factors. The present study aimed to characterize the molecular interactions between eIF-4E and the other subunits of eIF-4F and to similarly characterize the molecular interactions between eIF-4E and the 4E-BPs. A 49-amino-acid region of eIF-4 gamma, located in the N-terminal side of the site of cleavage by Picornaviridae protease 2A, was found to be sufficient for interacting with eIF-4E. Analysis of deletion mutants in this region led to the identification of a 12-amino-acid sequence conserved between mammals and Saccharomyces cerevisiae that is critical for the interaction with eIF-4E. A similar motif is found in the amino acid sequence of the 4E-BPs, and point mutations in this motif abolish the interaction with eIF-4E. These results shed light on the mechanisms of eIF-4F assembly and on the translational regulation by insulin and growth factors.