The Genome-linked Protein of Picornaviruses. VIII. Complete Amino Acid Sequence of Poliovirus VPg and Carboxy-terminal Analysis of its Precursor, P3-9

VPg, the genome-linked protein of poliovirus, and its putative precursor P3-9, were radiolabelled and subjected to carboxypeptidase-A digestion. The release of amino acids was followed by identification and quantification on an amino acid analyser. Both proteins were found to be co-terminal with a sequence of -valyl-glutamine-COOH, an observation that provides further evidence that host cell trimming of virus-specific peptides does not play a role in poliovirus protein processing. Radiolabelled VPg was subjected to automated Edman degradation. The combined results complete the structural analysis of VPg, a polypeptide 22 amino acids in length with a molecular weight of 2354. Only one form of VPg has been found linked to virion RNA and it originates by a cleavage at glutaminyl-glycine pairs at both termini. The observation is consistent with other cleavages found in the virus processing scheme.