(13.5 kilobases total), which encode 11 proteins (HA, NA, NP, M1, M2, NS1, NEP, PA, PB1, PB1-F2, PB2). The best-characterised of these viral proteins are hemagglutinin and neuraminidase , two large glycoproteins found on the outside of the viral particles. Neuraminidase is an enzyme involved in the release of progeny virus