Taxonomic Structure of the Family
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Family |
Sequiviridae |
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Genus |
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Genus |
Particles are isometric, about 30 nm in diameter (Fig. 1).
Physicochemical and Physical Properties
The main virion component sediments at 150-190S, contains about 40% RNA and has a correspondingly high equilibrium density in cesium salts. Some preparations also contain a slower sedimenting (about 60S), less dense particle.
The main virion component contains one molecule of infective, positive sense ssRNA, 9-12 kb in size. Genome RNA of sequiviruses is not polyadenylated but the genome RNA of waikaviruses is. Infectivity is protease-sensitive and a 5-linked VPg molecule is probably present. There are some reports of an approximately 1 kb RNA being present in the 60S particles.
Virions contain three major species with Mr of about 32, 26 and 23 103. Particles of some waikaviruses are thought to contain other proteins which may be derived from one of the three major proteins. Virion and non-structural proteins arise by proteolytic cleavage of a polyprotein.
None reported.
None reported.
Genome Organization and Replication
The virus genome consists of a single infective ssRNA containing one major ORF which encodes a polyprotein of about 3,000 to 3,500 aa. The structural proteins are in the N-terminal half of the polyprotein but are separated from the N-terminus by polypeptide(s) of Mr = 40-60 103. Sequences downstream of the structural proteins contain domains characteristic of proteins with nucleoside triphosphate binding, protease and RNA polymerase activities. Small (c.1 kb) sgRNA has been found in virion preparations of waikaviruses that may correspond to small ORFs downstream of the major large ORF (Fig. 2).
Polyclonal sera contain antibodies to all virion proteins.
Natural host ranges are restricted. Transmission is in the semi-persistent manner by aphids or, for two of three waikavirus species, by leafhoppers. A helper protein is needed which may be self-encoded (Waikavirus) or encoded by a helper virus (Sequivirus).
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