Recombinant Influenza A virus Nucleoprotein (NP)

Function

Encapsidates the negative strand viral RNA, protecting it from nucleases. The encapsidated genomic RNA is termed the ribonucleoprotein (RNP) and serves as template for transcription and replication. The RNP needs to be localized in the host nucleus to start an infectious cycle, but is too large to diffuse through the nuclear pore complex. NP comprises at least 2 nuclear localization signals that are responsible for the active RNP import into the nucleus through cellular importin alpha/beta pathway. Later in the infection, nclear export of RNPs are mediated through viral proteins NEP interacting with M1 which binds nucleoproteins. It is possible that nucleoprotein binds directly host exportin-1/XPO1 and plays an active role in RNPs nuclear export. M1 interaction with RNP seems to hide nucleoprotein's nuclear localization signals. Soon after a virion infects a new cell, M1 dissociates from the RNP under acidification of the virion driven by M2 protein. Dissociation of M1 from RNP unmasks nucleoprotein's nuclear localization signals, targeting the RNP to the nucleus

Subcellular Location

Virion; Host nucleus

Subunit

Homomultimerizes to form the nucleocapsid. May bind host exportin-1/XPO1. Binds to viral genomic RNA. Protein-RNA contacts are mediated by a combination of electrostatic interactions between positively charged residues and the phosphate backbone and planar interactions between aromatic side chains and bases

• Reinhardt U. et al. Sequence of the nucleoprotein (NP) gene of the influenza A virus reassortant 81/HO, carrying the NP originally derived from A/Hong Kong/1/68 (H3N2). — Nucleic Acids Res. (1989)
• Brown E.G. et al. Pattern of mutation in the genome of influenza A virus on adaptation to increased virulence in the mouse lung: identification of functional themes. — Proc. Natl. Acad. Sci. U.S.A. (2001)