Roles of the Picornaviral 3C Proteinase in the Viral Life Cycle and Host Cells

Sun, Di; Chen, Shun; Cheng, Anchun; Wang, Mingshu

Protein synthesis in host cells depends on the 5 1 terminal cap structure and several cap-binding proteins, but viral mRNA utilizes an IRES for translation ( Figure 4) . Firstly, the m7G(5 1 )ppp(5 1 )N structure is recognized by a translation initiation factor (eIF4F), which is composed of the eIF4G scaffolding protein, the eIF4E cap-binding protein and the eIF4A RNA helicase to initiate cellular mRNA translation. The 43S preinitiation complex (PIC) contains eIFs, including eIF1, eIF1A, eIF3, eIF5 and the ternary complex (eIF2-GTP-Met-tRNA), together with the 40S ribosomal subunit. The binding of eIF4F to the cap and the binding of PABP to the poly (A) tail circularizes the mRNA to activate the mRNA. The 43S ribosome then binds near the cap and scans the 5 1 -UTR for an AUG codon [57] . Identification of the AUG start codon constitutes the first stage of the translation of cellular mRNA ( Figure 4B ).