A second virus-encoded proteinase involved in proteolytic processing of poliovirus polyprotein.

The poliovirus polyprotein is cleaved at three different amino acid pairs. Viral polypeptide 3C is responsible for processing at the most common pair (glutamineglycine). We have found that a cDNA fragment encoding parts of the capsid protein region (P1) and the nonstructural protein region (P2), and including the P1-P2 processing site (tyrosine-glycine), can be expressed in E. coli. The translation product was correctly processed. Disruption of the coding sequence of 2A, a nonstructural polypeptide mapping carboxy-terminal to the tyrosine-glycine cleavage site, by linker mutagenesis or deletion, prevented processing. Deletion of the adjacent polypeptide 2B had no such effect. Antibodies against 2A specifically inhibited processing at the 3C'-3D' processing site (tyrosine-glycine) in vitro. We conclude that poliovirus encodes the second proteinase 2A, which processes the polyprotein at tyrosine-glycine cleavage sites.