Virus-specific polypeptides of human parainfluenza virus type 4 and their synthesis in infected cells

We have studied the structural components of human parainfluenza virus type 4A (PIV-4A) and identified some virus-specific polypeptides by immunoprecipitation with polyclonal and monoclonal antibodies followed by one- or two-dimensional SDS-PAGE. HN polypeptides existed as monomer, disulfide-linked dimer, and disulfide-linked larger oligomer in cells infected with PIV-4A. Interestingly, the nonreduced NP, the nonreduced fusion, and the reduced F1 proteins migrated as doublets. Two F1 polypeptides were derived from different F1 + 2 proteins which migrated separately under nonreducing condition. In Vero cells infected with two strains of PIV-4A, two lower-molecular-weight proteins related to NP were detected. Oligopeptide patterns of the lower-molecular-weight protein were similar to those of NP protein synthesized in primary monkey kidney cells. The NP-related low-molecular-weight protein(s) was immunoprecipitated by 1 of 11 monoclonal antibodies against mumps virus NP protein. The MAb also reacted with NP proteins of PIV-2 and SV5. Thus, the epitope recognized by the MAb was common among PIV-2, PIV-4, mumps virus, and SV5, suggesting that the epitope might have an important biological function. However, the MAb did not react with the intact NP protein from cells infected with PIV-4, indicating that the epitope of PIV-4A was presented only when NP was cleaved. Phosphorylation was demonstrated for NP and P proteins.