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. Author manuscript; available in PMC: 2022 Mar 14.
Published in final edited form as: J Cell Immunol. 2021;3(5):296–304. doi: 10.33696/immunology.3.110

Figure 1: Canonical and non-canonical mechanisms of translation initiation.

Figure 1:

(A) Schematic representation of canonical or cap-dependent translation initiation. Translation initiation factors eIF1, eIF1A, eIF2, eIF3, eIF5, eIF4E, eIF4A, eIF4B, eIF4G are labeled as numbers. Small ribosomal subunit is marked as 40S. The 43S PIC (40S, eIF1, eIF1A, eIF3, eIF5, and eIF2•GTP•Met-tRNAiMet) is recruited to the 5’-end of mRNA via the cap-binding protein eIF4E bound to m7G-cap (red circle), and RNA helicase eIF4A is recruited to the scaffold protein eIF4G. (B) IRES-mediated translation initiation. Ribosomes are recruited internally (downstream of 5’-end) to mRNA and positioned adjacent to or on the initiation codon. IRES is represented as a complex secondary RNA structure. (C) CITE-directed translation. Translation machinery is recruited by eIF4G to the extreme 5’-end of the mRNA independently of capping. CITEs utilize 5’-end scanning similar to canonical translation but unlike IRES-mediated translation initiation mechanism. (B and C) Cap-binding factor eIF4E does not participate in IRES- and CITE-mediated translation initiation mechanisms.