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 5' end, and suggest a model for how eIF4F-mRNA dynamics establish mRNA sensitivity to translational control processes.