The influenza A virus is the leading cause of annual influenza epidemics and occasional influenza pandemics. NP of influenza A virus plays a central role in viral replication. As a structural protein with no intrinsic enzymatic activity, it is the most abundant viral protein in infected cells. Monomeric NP is a 56 kDa protein with a patch of basic residues capable of binding to a single-strand RNA. NP also contains nuclear localization signals (NLS) and nuclear export signals (NES). The Influenza A virus nucleoprotein (NP) is the major protein component of the genomic viral ribonucleoprotein (vRNP) complexes, which are the replication- and transcription-competent units of Influenza viruses. Early during infection, NP mediates import of vRNPs into the host cell nucleus where viral replication and transcription take place; also newly synthesized NP molecules are targeted into the nucleus, enabling coreplicational assembly of progeny vRNPs.