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

mRNA 5 ' cap recognition by eIF4F is a key element of eukaryotic translational control. Kinetic differences in eIF4F-mRNA interactions have long been proposed to mediate translation-efficiency differences between mRNAs, and recent transcriptome-wide studies have revealed significant heterogeneity in eIF4F engagement with differentially-translated mRNAs. However, detailed kinetic information exists only for eIF4F interactions with short model RNAs. We developed and applied single-molecule fluorescence approaches to directly observe real-time Saccharomyces cerevisiae eIF4F subunit interactions with full-length polyadenylated mRNAs. We found that eIF4E-mRNA association rates linearly anticorrelate with mRNA length. eIF4G-mRNA interaction accelerates eIF4E-mRNA association in proportion to mRNA length, as does an eIF4F-independent activity of eIF4A, though cap-proximal secondary structure still plays an important role in defining the final association rates. eIF4F-mRNA interactions remained dominated by effects of eIF4G, but were modulated to different extents for different mRNAs by the presence of eIF4A and ATP. We also found that eIF4A-catalyzed ATP hydrolysis ejects eIF4E, and likely eIF4E center dot eIF4G from the mRNA after initial eIF4F center dot mRNA complex formation, suggesting a mechanism to prepare the mRNA 5 ' end for ribosome recruitment. Our results support a role for mRNA-specific, factor-driven eIF4F association rates in kinetically controlling translation.

Automated summary

Studies have shown that the interaction between eIF4F and mRNA is regulated by mRNA length, cap-proximal secondary structure, eIF4A, and ATP. The activities of eIF4G and eIF4A accelerate the association rate of eIF4E with mRNA, playing a crucial role in translation.