Dynamic Interaction of Eukaryotic Initiation Factor 4G1 (eIF4G1) with eIF4E and eIF1 Underlies Scanning-Dependent and -Independent Translation

ABSTRACT

Translation initiation of most mRNAs involves m7G-cap binding, ribosomal scanning, and AUG selection. Initiation from an m7G-cap-proximal AUG can be bypassed resulting in leaky scanning, except for mRNAs bearing the translation initiator of short 5′ untranslated region (TISU) element. m7G-cap binding is mediated by the eukaryotic initiation factor 4E (eIF4E)-eIF4G1 complex. eIF4G1 also associates with eIF1, and both promote scanning and AUG selection. Understanding of the dynamics and significance of these interactions is lacking. We report that eIF4G1 exists in two complexes, either with eIF4E or with eIF1. Using an eIF1 mutant impaired in eIF4G1 binding, we demonstrate that eIF1-eIF4G1 interaction is important for leaky scanning and for avoiding m7G-cap-proximal initiation. Intriguingly, eIF4E-eIF4G1 antagonizes the scanning promoted by eIF1-eIF4G1 and is required for TISU. In mapping the eIF1-binding site on eIF4G1, we unexpectedly found that eIF4E also binds it indirectly. These findings uncover the RNA features underlying regulation by eIF4E-eIF4G1 and eIF1-eIF4G1 and suggest that 43S ribosome transition from the m7G-cap to scanning involves relocation of eIF4G1 from eIF4E to eIF1.

KEYWORDS:

• leaky scanning
• TISU
• eIF1
• eIF4E
• eIF4G1
• translation initiation

View publisher note:

Articles of Significant Interest in This Issue

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at https://doi.org/10.1128/MCB.00139-18.

ACKNOWLEDGMENTS

We are grateful to Ariel Stanhill for the eIF1 antibodies.

This study was supported by grants from the Minerva Foundation (grant 712278 [R.D.]) and the Israel Science Foundation (grant 843/17 [R.D.]), an Innovative Award from the Terry Johnson Cancer Center, KSU (K.A.), a KU-COBRE Protein Structure and Function Pilot Grant (P30GM110761 [K.A.]), and an NSF research grant (grant 1412250 [K.A.]). R.D. is the incumbent of the Ruth and Leonard Simon Chair of Cancer Research.

R.D. and O.H. conceived and designed the study, analyzed the data, and wrote the paper. O.H. carried out most of the experiments. U.S., A.T.-B.H., A.B., A.U., and A.W. performed part of the experiments. H.H. and K.A. provided the structure of human eIF1 with the marked eIF4G1 contacting residues.

We declare that we have no conflict of interest.