Heterogeneous forms of polymerase proteins exist in influenza A virus-infected cells

In influenza virus-infected cells a virus coded polymerase that consists of three polypeptide subunits, namely PB1, PB2 and PA, mediates both transcription and replication. Radioimmunoprecipitation with monospecific antisera to each of the polymerase proteins revealed additional forms of PB1 and PA proteins in infected cells. PA antiserum detected two additional proteins of 62k and 60k and PB1 antiserum recognized two additional proteins of 85k and 70k. Further investigation was carried out on the 62k PA and 85k PB1 related proteins. Limited proteolysis peptide mapping showed that these proteins are subsets of their normal counter-parts. These new forms of polymerase proteins are designated as "b" forms (PAb and PB1b) to distinguish them from the previously recognized forms designated as "a" forms (PAa and PB1a). Both PAb and PB1b proteins were found in cells infected with all the influenza type A viruses tested indicating that they are evolutionarily conserved. Pulse chase experiments showed that the "b" forms are not derived from "a" forms. This suggested that "b" forms are translated independently. The "b" forms were not detected in purified virus but were found to be associated with intracellular RNP templates, suggesting a role for these proteins in intracellular virus replication events.