Internal Ribosome Entry Site-Mediated Translation

In eukaryotes, the major mechanism of translation initiation involves recognition of the cap structure at the 5′ end of the mRNA by a cap-binding protein, eIF4E. An internal ribosome entry site (IRES) is a specialized RNA element that recruits the translation machinery to an internal position of the mRNA in a 5′-end independent fashion. The best-characterized viral IRESs initiate translation by several mechanisms that require different sets of canonical initiation factors. Furthermore, IRES activity can be modulated by IRES transacting factors. Albeit controversial, some cellular mRNAs were reported to contain IRESs, as they are expressed in cells under stress and other conditions when cap-dependent initiation is inhibited.