Structure of the RNA specialized translation initiation element that recruits eIF3 to the 5'-UTR of c-Jun.

Specialized translation initiation is a novel form of regulation of protein synthesis, whereby RNA structures within the 5′-UTR regulate translation rates of specific mRNAs. Similar to internal ribosome entry sites (IRESs), specialized translation initiation requires the recruitment of eukaryotic initiation factor 3 (eIF3), but also requires cap recognition by eIF3d, a new 5′-m7GTP recognizing protein. How these RNA structures mediate eIF3 recruitment to affect translation of specific mRNAs remains unclear. Here, we report the nuclear magnetic resonance (NMR) structure of a stem-loop within the c-JUN 5′ UTR recognized by eIF3 and essential for specialized translation initiation of this well-known oncogene. The structure exhibits similarity to eIF3 recognizing motifs found in hepatitis C virus (HCV)–like IRESs, suggesting mechanistic similarities. This work establishes the RNA structural features involved in c-JUN specialized translation initiation and provides a basis to search for small molecule inhibitors of aberrant expression of the proto-oncogenic c-JUN.