Belongs to the influenza viruses nucleoprotein family.
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.
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.
Late in virus-infected cells, may be cleaved from a 56-kDa protein to a 53-kDa protein by a cellular caspase. This cleavage might be a marker for the onset of apoptosis in infected cells or have a specific function in virus host interaction.
Belongs to the influenza C protein M1 family.
Homodimer; disulfide-linked. Homotetramer; disulfide-linked.
Ion channel, which might have a role in genome packaging and uncoating processes.
Ser-337 is the major site of phosphorylation, Ser-362 being a minor one.
Belongs to the influenza viruses hemagglutinin family.
Binds to the N-acetyl-9-O-acetylneuraminic acid residues on the cell surface, bringing about the attachment of the virus particle to the cell. Plays a major role in the determination of host range restriction and virulence. Class I viral fusion protein. Responsible for penetration of the virus into the cell cytoplasm by mediating the fusion of the membrane of the endocytosed virus particle with the endosomal membrane. Low pH in endosomes induce an irreversible conformational change in HEF2, releasing the fusion hydrophobic peptide. Several trimers are required to form a competent fusion pore. Displays a receptor-destroying activity which is a neuraminidate-O-acetyl esterase. This activity cleaves off any receptor on the cell surface, which would otherwise prevent virions release. These cleavages prevent self-aggregation and ensure the efficient spread of the progeny virus from cell to cell.
Homotrimer of disulfide-linked HEF1-HEF2.
In natural infection, inactive HEF is matured into HEF1 and HEF2 outside the cell by one or more trypsin-like, arginine-specific endoprotease.
Belongs to the influenza viruses NEP family.
Interacts with protein M1. May interact with host nucleoporin RAB/HRB and exportin XPO1/CRM1.
Mediates the nuclear export of encapsidated genomic RNAs (ribonucleoproteins, RNPs). Acts as an adapter between viral RNPs complexes and the nuclear export machinery of the cell. Possesses no intrinsic RNA-binding activity, but includes a C-terminal M1-binding domain. This domain is believed to allow recognition of RNPs bound to the protein M1. Since protein M1 is not available in large quantities before late stages of infection, such an indirect recognition mechanism probably ensures that genomic RNPs are not exported from the host nucleus until sufficient quantities of viral mRNA and progeny genomic RNA have been synthesized. Furthermore, the RNPs enter the host cytoplasm only when associated with the M1 protein that is necessary to guide them to the plasma membrane. May down-regulate viral RNA synthesis when overproduced.
Belongs to the influenza viruses PA family.
Influenza RNA polymerase is composed of three subunits: PB1, PB2 and PA. Interacts (via C-terminus) with PB1 (via N-terminus).
Phosphorylated on serines and threonines by host kinases, including human casein kinase II.
Plays an essential role in viral RNA transcription and replication by forming the heterotrimeric polymerase complex together with PB1 and PB2 subunits. The complex transcribes viral mRNAs by using a unique mechanism called cap-snatching. It consists in the hijacking and cleavage of host capped pre-mRNAs. These short capped RNAs are then used as primers for viral mRNAs. The PB2 subunit is responsible for the binding of the 5' cap of cellular pre-mRNAs which are subsequently cleaved after 10-13 nucleotides by the PA subunit that carries the endonuclease activity.
Belongs to the influenza C viruses NS1 family.
Prevents the establishment of the cellular antiviral state initiated by host RIGI, which normally triggers the antiviral transduction signal that leads to the activation of type I IFN genes by transcription factors IRF3 and IRF7. Participates also in the up-regulation of the splicing of viral mRNAs.
The NS1 protein of strain C/Ann Arbor/1/50-pi is phosphorylated.
The strain C/Ann Arbor/1/50-pi causes persistent infection.
Belongs to the influenza viruses polymerase PB1 family.
Influenza RNA polymerase is composed of three subunits: PB1, PB2 and PA. Interacts (via N-terminus) with PA (via C-terminus). Interacts (via C-terminus) with PB2 (via N-terminus); this interaction is essential for transcription initiation.
RNA-dependent RNA polymerase which is responsible for replication and transcription of virus RNA segments. The transcription of viral mRNAs occurs by a unique mechanism called cap-snatching. 5' methylated caps of cellular mRNAs are cleaved after 10-13 nucleotides by PA. In turn, these short capped RNAs are used as primers by PB1 for transcription of viral mRNAs. During virus replication, PB1 initiates RNA synthesis and copy vRNA into complementary RNA (cRNA) which in turn serves as a template for the production of more vRNAs.
Belongs to the influenza viruses PB2 family.
Influenza RNA polymerase is composed of three subunits: PB1, PB2 and PA. Interacts (via N-terminus) with PB1 (via C-terminus). Interacts with nucleoprotein NP (via N-terminus).
Plays an essential role in transcription initiation and cap-stealing mechanism, in which cellular capped pre-mRNAs are used to generate primers for viral transcription. Recognizes and binds a wide range of cap structures of target pre-RNAs which are subsequently cleaved after 10-13 nucleotides by the viral protein PA. Plays a role in the initiation of the viral genome replication and modulates the activity of the ribonucleoprotein (RNP) complex.