Figure 1.

Cap-dependent translation initiation. When an initiator tRNA binds to guanosine triphosphate (GTP)-bound eukaryotic initiation factor (eIF2), the complex can further recruit eIF1, eIF1A, eIF3, eIF5, and 40S ribosome to form 43S pre-initiation complex (43S PIC). eIF4F, composed of eIF4A, eIF4E, and eIF4G, facilitates the recruitment of mRNA to 43S PIC. Then, eIF4E binds to the 5′-cap of mRNA, and eIF4G recruits poly(A)-binding protein (PABP), which binds to poly(A) on mRNA on the 3′-end, thus circularizing the mRNA to stabilize it for translation. eIF4A functions as a helicase and may facilitate mRNA scanning to find the initiation codon AUG. Once the codon is found by 43S PIC, eIFs are released and the 60S ribosomal subunit joins the assembly to generate protein synthesis-ready 80S ribosome ready for translation elongation.