Once the synthesis of several thousands of positive RNA molecules is performed, the late phase of translation takes place, giving rise also during this period to a great amount of viral proteins, some of which will participate in virus morphogenesis. This late phase of infection is preceded by the abrogation of cellular mRNA translation, such that only viral proteins are being synthesized late in the PV life cycle [14] . In the case of picornaviruses, transcription is dependent on continuous viral protein synthesis [28] . Thus, inhibition of viral mRNA translation provokes the sudden blockade of viral RNA synthesis. Moreover, translation is coupled to transcription, such that viral RNAs transfected Journal of Biomedicine and Biotechnology Figure 1 : (a) Structure of poliovirus genome and proteolytic processing of its polyprotein. The PV genome consists of a single-stranded, positive-sense polarity RNA molecule, which encodes a single polyprotein. The 5 nontranslated region (NTR) is covalently linked to the viral protein VPg. The PV genome is polyadenylated (A n ) in its 3 end. The polyprotein contains four structural (P1) and seven nonstructural (P2 and P3) proteins that are released from the polypeptide chain by proteolytic processing mediated by the viral-encoded proteinases 2A pro and 3C pro /3CD pro . The intermediate products of processing 2BC, 3CD, and 3AB exhibit functions distinct from those of their respective final cleavage products. The alternative cleavage carried out by 2A pro rendering the mature products 3C and 3D is also shown. (b) Once the ribosome has synthesized the PV 2A pro sequence and continues translation on the P2 region, the autocatalytic activity of PV 2A pro is manifested by cleaving itself at its amino terminus still on the nascent polypeptide chain. This cleavage liberates the P1 precursor that will render the capsid proteins on subsequent proteolytic events catalyzed by 3C pro or 3CD pro . Cleavage at the carboxy terminus of PV 2A pro on the P2 precursor is accomplished by PV 3C pro , leaving free 2A pro and generating the 2BC precursor.