Influenza A viral nucleoprotein (NP) plays a critical role in virus replication and host adaptation. The influenza A virus nucleoprotein (NP) is an essential multifunctional protein that encapsidates the viral genome and functions as an adapter between the virus and the host cell machinery. NPs from all strains of influenza A viruses contain two nuclear localization signals (NLSs): a well-studied monopartite NLS1 and a less-characterized NLS2, thought to be bipartite. The nucleocapsid is a complex of the viral nucleoprotein, RNA, and several other viral proteins. The nucleoprotein forms large, RNA-bound, helical filaments and acts as a scaffold for additional viral proteins.