The Multifaceted Poliovirus 2A Protease: Regulation of Gene Expression by Picornavirus Proteases
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 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 2Apro and 3Cpro /3CDpro. 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 2Apro rendering the mature products 3C′ and 3D′ is also shown. (b) Once the ribosome has synthesized the PV 2Apro sequence and continues translation on the P2 region, the autocatalytic activity of PV 2Apro 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 3Cpro or 3CDpro. Cleavage at the carboxy terminus of PV 2Apro on the P2 precursor is accomplished by PV 3Cpro, leaving free 2Apro and generating the 2BC precursor.
