title: Structure of the Rift Valley fever virus nucleocapsid protein reveals another architecture for RNA encapsidation.
abstract: Rift Valley fever virus (RVFV) is a negative-sense RNA virus (genus Phlebovirus, family Bunyaviridae) that infects livestock and humans and is endemic to sub-Saharan Africa. Like all negative-sense viruses, the segmented RNA genome of RVFV is encapsidated by a nucleocapsid protein (N). The 1.93-A crystal structure of RVFV N and electron micrographs of ribonucleoprotein (RNP) reveal an encapsidated genome of substantially different organization than in other negative-sense RNA virus families. The RNP polymer, viewed in electron micrographs of both virus RNP and RNP reconstituted from purified N with a defined RNA, has an extended structure without helical symmetry. N-RNA species of approximately 100-kDa apparent molecular weight and heterogeneous composition were obtained by exhaustive ribonuclease treatment of virus RNP, by recombinant expression of N, and by reconstitution from purified N and an RNA oligomer. RNA-free N, obtained by denaturation and refolding, has a novel all-helical fold that is compact and well ordered at both the N and C termini. Unlike N of other negative-sense RNA viruses, RVFV N has no positively charged surface cleft for RNA binding and no protruding termini or loops to stabilize a defined N-RNA oligomer or RNP helix. A potential protein interaction site was identified in a conserved hydrophobic pocket. The nonhelical appearance of phlebovirus RNP, the heterogeneous approximately 100-kDa N-RNA multimer, and the N fold differ substantially from the RNP and N of other negative-sense RNA virus families and provide valuable insights into the structure of the encapsidated phlebovirus genome.
authors.affiliation: Life Sciences Institute, University of Michigan, Ann Arbor, MI 48109, USA.
authors.forename: Donald D
authors.initials: DD
authors.lastname: Raymond
authors.forename: Mary E
authors.initials: ME
authors.lastname: Piper
authors.forename: Sonja R
authors.initials: SR
authors.lastname: Gerrard
authors.forename: Janet L
authors.initials: JL
authors.lastname: Smith
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D017931:DNA Primers / Q000235:genetics; D006801:Humans; D046911:Macromolecular Substances / Q000737:chemistry; D046529:Microscopy, Electron, Transmission; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D019590:Nucleocapsid Proteins / Q000737:chemistry* / Q000235:genetics / Q000648:ultrastructure; D016856:Phlebovirus / Q000235:genetics; D054730:Protein Interaction Domains and Motifs; D055503:Protein Multimerization; D012367:RNA, Viral / Q000737:chemistry* / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000648:ultrastructure; D012296:Rift Valley fever virus / Q000737:chemistry* / Q000235:genetics / Q000502:physiology / Q000648:ultrastructure; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity; D019065:Virus Assembly
chemical_list: D017931:DNA Primers; D046911:Macromolecular Substances; D019590:Nucleocapsid Proteins; D012367:RNA, Viral; D011993:Recombinant Fusion Proteins