As influenza viruses bud from the plasma membrane of infected cells, complete virions are not seen inside cells. In polarized epithelial cells, assembly and budding of influenza occurs from the apical plasma membrane (Schmitt, 2004). For efficient assembly, all virion components must accumulate at the budding site, and it is believed that the viral glycoprotein accumulation determines the site of virus assembly and budding (Nayak, 2004). M1 is thought to be the bridge between the envelope glycoproteins and the RNPs for assembly (Schmitt, 2004). M2 is also required, because if it is not present RNPs are not packaged into budding virions (McCown, 2005), however it role is not known.