Abstract
VPg is a virus-encoded protein covalently attached to the 5'' end of poliovirus virion RNA. Antibody prepared against chemically synthesized VPg was used to detect 2 forms of VPg in infected cells. Both forms were specifically immunoprecipitated from lysates of infected human cervical carcinoma HeLa cells labeled with [3H]-leucine. One appears to be unmodified VPg because it had the same electrophoretic mobility as synthetic VPg. The other had a larger apparent MW than VPg and could be labeled in vivo with 32Pi. Its structure is VPg-pUpU, the UMP dinucleotide being attached to VPg via a phosphodiester bond to tyrosine, the 3rd amino acid from the NH2 terminus of VPg. This structure is identical to that found at the 5'' end of virion and minus-strand RNA.