Article

Architecture of ribonucleoprotein complexes in influenza A virus particles

University of California, Davis, Davis, California, United States
Nature (Impact Factor: 42.35). 02/2006; 439(7075):490-2. DOI: 10.1038/nature04378
Source: PubMed

ABSTRACT In viruses, as in eukaryotes, elaborate mechanisms have evolved to protect the genome and to ensure its timely replication and reliable transmission to progeny. Influenza A viruses are enveloped, spherical or filamentous structures, ranging from 80 to 120 nm in diameter. Inside each envelope is a viral genome consisting of eight single-stranded negative-sense RNA segments of 890 to 2,341 nucleotides each. These segments are associated with nucleoprotein and three polymerase subunits, designated PA, PB1 and PB2; the resultant ribonucleoprotein complexes (RNPs) resemble a twisted rod (10-15 nm in width and 30-120 nm in length) that is folded back and coiled on itself. Late in viral infection, newly synthesized RNPs are transported from the nucleus to the plasma membrane, where they are incorporated into progeny virions capable of infecting other cells. Here we show, by transmission electron microscopy of serially sectioned virions, that the RNPs of influenza A virus are organized in a distinct pattern (seven segments of different lengths surrounding a central segment). The individual RNPs are suspended from the interior of the viral envelope at the distal end of the budding virion and are oriented perpendicular to the budding tip. This finding argues against random incorporation of RNPs into virions, supporting instead a model in which each segment contains specific incorporation signals that enable the RNPs to be recruited and packaged as a complete set. A selective mechanism of RNP incorporation into virions and the unique organization of the eight RNP segments may be crucial to maintaining the integrity of the viral genome during repeated cycles of replication.

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    • "composed mostly of the NP protein, which wraps eight different RNA segments of the influenza A genome. Additionally , RNPs contain about 50 copies per virion of RNA-dependent RNA polymerase, which in case of influenza A virus is a complex of three proteins: PB1, PB2 and PA (Noda et al., 2006; Boivin et al., 2010). "
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    • "Less frequently the small capsular particles are oriented with their long axis perpendicular to the ice film (Fig. 1b). This shows the envelope glycoproteins and a layer formed by the M1 surrounding eight RNPs in a 7 + 1 arrangement previously identified in plastic sections of budding virus [8] [9] which likely correspond to the eight genomic segments. In more elongated Udorn virions these are observed to be at one end [4]. "
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