A membrane-associated precursor to poliovirus VPg identified by immunoprecipitation with antibodies directed against a synthetic heptapeptide

A synthetic heptapeptide corresponding to the C-terminal sequence of the poliovirus genome protein (VPg) has been linked to bovine serum albumin and used to raise antibodies in rabbits. These antibodies precipitate not only VPg but also at least two more virus-specific polypeptides. The smaller polypeptide, denoted P3–9 (12,000 daltons), has been mapped by Edman degradation and by fragmentation with cyanogen bromide and determined to be the N-terminal cleavage product of polypeptide P3-1b, a precursor to the RNA polymerase. P3–9 contains the sequence of the basic protein VPg (22 amino acids) at its C terminus. As predicted by the known RNA sequence of poliovirus, P3–9 also contains a hydrophobic region of 22 amino acids preceding VPg, an observation suggesting that P3–9 may be membrane-associated. This was confirmed by fractionation of infected cells in the presence or absence of detergent. We speculate that P3–9 may be the donor of VPg to RNA chains in the membrane-bound RNA replication complex.