Identification of a second protein (M2) encoded by RNA segment 7 of influenza virus

Recent analyses of the nucleotide sequences of RNA segment 7 of influenza virus from two strains of infuenza A virus (PR/8/34 and Udorn/72) have shown that in addition to the reading frame coding for the membrane protein (M₁) there is a second overlapping open reading frame that could code for 97 amino acids [Winter and Fields (1980). Nucleic Acids Res.8, 1965–1974;Allen et al. (1980). Virology107, 548–551;Lamb and Lai (1981). Virology112, 746–751]. We have identified such a protein (M₂) in infected cells and shown that it is synthesized from a separate mRNA. Hybrid-arrested translation experiments and the use of recombinant viruses of defined genome composition have demonstrated by both biochemical and genetic approaches that protein M₂ is coded for by RNA segment 7. Peptide mapping studies have shown that M₁ and M₂ are distinct proteins, and the peptide maps can be correlated with the nucleotide sequences coding for M₁ and M₂.