The Structure of Native Influenza Virion Ribonucleoproteins

Abstract

The influenza viruses cause annual epidemics of respiratory disease and occasional pandemics, which constitute a major public-health issue. The segmented negative-stranded RNAs are associated with the polymerase complex and nucleoprotein (NP), forming ribonucleoproteins (RNPs), which are responsible for virus transcription and replication. We describe the structure of native RNPs derived from virions. They show a double-helical conformation in which two NP strands of opposite polarity are associated with each other along the helix. Both strands are connected by a short loop at one end of the particle and interact with the polymerase complex at the other end. This structure will be relevant for unraveling the mechanisms of nuclear import of parental virus RNPs, their transcription and replication, and the encapsidation of progeny RNPs into virions.

Isolation and characterization of the positive-sense replicative intermediate of a negative-strand RNA virus

“…We observed a varying diameter of the loop at the terminus of the cRNP, with three to seven NP molecules being present within the loop. This observation is consistent with previous reports that the loop end of the vRNP comprises five to eight NP molecules in one study (3) and three NP molecules in another study (2). In contrast to previous studies, which analyzed a mixture of vRNPs corresponding to RNA segments of various lengths, here we analyze one particular cRNP with an RNA segment of a defined length.…”

“…Our data revealed that the replicative intermediate of influenza virus exists as an individual structured particle that comprises cRNA, NP, and RdRp. We observed that the cRNP particle contains three major domains, the central filament and two distinct termini, one terminus harboring a loop and the other a structure that we interpret as the RdRp, on the basis of analogy to previously published structures of vRNPs (2,3). The central filament exhibited a helical arrangement, similar to the reported vRNP filament structure (2,3) in which the helical arrangement of the filament is facilitated by NP-NP interactions.…”

“…The genomic viral RNA (vRNA) molecules of negative-strand RNA viruses are assembled into viral ribonucleoprotein particles (vRNPs) containing an oligomer of nucleoprotein (NP) and the RNA-dependent RNA polymerase (RdRp), which is responsible for transcription and replication of the viral genome. High-resolution structures of the genomic ribonucleoproteins of negative-strand RNA viruses have been determined by means of EM, the best-studied example of which is the vRNP of influenza A virus (2,3).…”

“…One copy of the 250-kDa heterotrimeric RdRp, containing the polymerase basic 1 (PB1), polymerase basic 2 (PB2), and polymerase acidic (PA) subunits, binds at one end of the filament interacting with both the 5′ and the 3′ ends of the vRNA (2,3). Influenza viruses initiate infection by delivering these highly specialized RNA synthesis machines into the nucleus of a host cell for the expression of viral genes.…”

Helical capsids of plant viruses: architecture with structural lability

“…Three structurally dissimilar types of viral helical capsids have been studied so far: capsids of filamentous bacteriophages resembling, in structure and biogenesis, the type IV pili of bacterial cells (Russel et al, 1997); flexuous 'nucleocapsids' of negative-stranded RNA genomes representing regular RNA-protein complexes condensed into coiled structures (Albertini et al, 2006;Arranz et al, 2012;Longhi et al, 2015;Ruigrok et al, 2011); and capsids of numerous plant viruses (Stubbs & Kendall, 2012).…”