Segment 8 of the influenza virus genome is unique in coding for two polypeptides

In previous studies we showed that a ninth polypeptide with a molecular weight of ~11,000 (NS₂) found in influenza virus-infected cells was unique, that it could be synthesized in vitro, and that its expression in vivo required early protein synthesis. On the basis of these results we suggested that one of the eight genome RNA segments of influenza virus codes for two polypeptides. We describe here differences in the electrophoretic mobility of the NS₂ polypeptides of different strains of influenza A virus. These results provided further evidence that NS₂ is virus coded and also made possible genetic studies using recombinants between two virus strains (HK and PR8) whose NS₂ polypeptides differ. These studies showed that the gene for NS₂ reassorts with that of the nonstructural polypeptide NS₁, which is coded by genome segment 8. A mRNA for NS₂ has been separated from that of NS₁ and the other viral polypeptides by centrifugation and has been translated in vitro. Hybridization of genome segment 8 to the total mRNAs from infected cells specifically prevented the synthesis of NS₂ and NS₁. These results indicate that influenza virus genome segment 8 is transcribed into two separate mRNAs that code for two polypeptides, NS₁ and NS₂. Possible mechanisms for the transcription of the two mRNAs from either contiguous or overlapping genes are discussed.