FIGURE 3.

Mechanisms of 5′-UTR-mediated translational enhancement. A, according to the canonical model of cap-dependent eukaryotic ribosome recruitment, the only specific point of contact between the 5′-UTR and the translation machinery is the m⁷G cap, which is bound by eIF4E. B, other eIFs, including eIF4G, eIF4A, and eIF4B, have RNA-binding activity, which viral IRESs such as EMCV exploit for efficient cap-independent ribosome recruitment. C, cellular 5′-UTRs may also use translational enhancer elements (shown as color-coded boxes along the RNA) to recruit the translation machinery via either cap-stimulated or cap-independent pathways. Sequence-specific RBPs can bridge interactions between 5′-UTR elements and general translation factors.