mRNA- and factor-driven dynamic variability controls eIF4F-cap recognition for translation initiation

Abstract

mRNA 5′ cap recognition by eIF4F is a key step in eukaryotic translational control. While different mRNAs respond differently to eIF4F–directed regulation, the molecular basis for this variability remains unclear. We developed single-molecule fluorescence assays to directly observe eIF4F–mRNA interactions. We uncovered a complex interplay of mRNA features with factor activities that differentiates cap recognition between mRNAs. eIF4E–cap association rates are anticorrelated with mRNA length. eIF4A leverages ATP binding to differentially accelerate eIF4E–mRNA association; the extent of this acceleration correlates with translation efficiency in vivo. eIF4G lengthens eIF4E–cap binding to persist on the initiation timescale. The full eIF4F complex discriminates between mRNAs in an ATP-dependent manner. After eIF4F–mRNA binding, eIF4E is ejected from the cap by eIF4A ATP hydrolysis. Our results suggest features throughout mRNA coordinate in controlling cap recognition at the 5ʹ end, and suggest a model for how eIF4F–mRNA dynamics establish mRNA sensitivity to translational control processes.

The metaphorical swiss army knife: The multitude and diverse roles of HEAT domains in eukaryotic translation initiation

“…There is a critical distinction between the nonspecific interactions of eIF4G with mRNA and the stronger and specific interactions with various IRESs. Single-molecule fluorescence assays and RIP-seq experiments indicate that eIF4G orthologs bind nonspecifically and dynamically with mRNA ( 163–165 ). In contrast, the interactions of eIF4G and DAP5 with IRESs are structure- and/or sequence-specific, suggesting that common structural folds in RNA could dictate the interactions ( 59 , 132 , 160 , 166–171 ).…”