Matrix protein 2 forms a proton-selective channel that required for the release of the viral genome during entry. After binding receptors on the host cell surface, the virus enters the cell by endocytosis, which acidifies the endosome. The low pH causes an activation of the channels, which then allow the influx of protons into the viral particle. The acidity weakens the association of matrix protein 1 with the nucleoprotein, uncovering the nuclear localization sites, and facilitates viral uncoating. With the nuclear localization sites uncovered, the genome can migrate to the host nucleus. The M2 protein may also regulate and maintain the high pH in the lumen of the trans-Golgi network. For hemagglutinin (HA) proteins with polybasic cleavage sites, M2 activity could protect HA proteins from premature conformational changes in the trans-Golgi network