The (-) RNA genome of the
influenza A virus, eight segments in total, is encapsidated in the form of ribonucleoprotein (RNP) complexes. The nucleoprotein (NP), the major protein component of RNPs, binds along the entire length of each genomic RNA segment at a 24-nt interval, forming the double-helical RNP structures found in mature viruses. The viral polymerase, consisting of PA, PB1, and PB2 subunits, binds to the two RNA termini of the RNP.
As one of the most abundant proteins made in infected cells,
influenza virus NP has essential roles in many important viral processes, including intracellular trafficking of the viral genome, viral RNA replication, viral genome packaging, and virus assembly. The recently determined crystal structures of two NP trimers show an overall fold and an external RNA binding mode that are different from rhabdovirus NP, as confirmed by a new cryo-EM reconstruction of a mini-RNP. Site-directed mutagenesis and RNA binding assays have confirmed that a positively charged groove plays an important role in NP:RNA binding. Other exciting results from recent studies include NP oligomerization, NP RNA binding, NP intracellular trafficking, NP phosphorylation, and NP-supported viral RNA replication. These new findings have led to a more detailed model for RNP structure and assembly
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Labels: Influenza A virus, Influenza virus NP