Figure 3: Comparison between cap-dependent and IRES-dependent translation initiation of cellular mRNAs. In cap-dependent translation, initiation complex is formed on the 5′ end of mRNA with help of several eukaryotic initiation factors (eIFs). eIF4F-complex (eIF4E, eIF4G, and eIF4A) is recruited to the 5′m7G cap. The key interaction between eIF3 and eIF4G recruits the ribosome to the 5′ cap. In IRES-mediated translation, initiation complex is formed in the vicinity of the start codon with help of ITAFs and eIFs. For example, XIAP IRES interacts with eIF3 and recruits the ribosome via eIF3-PAIP1-PABP link [12]. IRES: internal ribosome entry site; PABP: poly(A) tail binding protein; PAIP1: PABP interacting protein 1; 40S: 40S ribosomal subunit; AUG: start codon.