Cellular translational enhancer elements that recruit eukaryotic initiation factor 3.

Translation initiation is a highly regulated process that broadly affects eukaryotic gene expression. Eukaryotic initiation factor 3 (eIF3) is a central player in canonical and alternative pathways for ribosome recruitment. Here, we have investigated how direct binding of eIF3 contributes to the large and regulated differences in protein output conferred by different 5'-untranslated regions (5' UTRs) of cellular mRNAs. Using an unbiased high-throughput approach to determine the affinity of budding yeast eIF3 for native 5' UTRs from 4252 genes, we demonstrate that eIF3 binds specifically to a subset of 5' UTRs that contain a short unstructured binding motif, AMAYAA. eIF3-binding mRNAs have higher ribosome density in growing cells and are preferentially translated under certain stress conditions, supporting the functional relevance of this interaction. Our results reveal a new class of translational enhancers and suggest a mechanism by which changes in core initiation factor activity enact mRNA-specific translation programs.