Reoviridae. Reoviridae

Description of Reoviridae adapted from ICTVdb Virion Properties Morphology Virions consist of a capsid, a core, and a nucleoprotein complex. During their life cycle, virions loose during the extracellular phase the sometimes observed intracellular envelope. Virus may be sequestered within inclusion bodies that are not occluded and typically contain one nucleocapsid, or occluded by protein bodies (in the case of Cypovirus). Virus initiating infection is occluded by a crystalline protein matrix of polyhedral shape. Each occlusion body contains several virions. Virus capsid is usually not enveloped, or enveloped when immature particles are budding into the endoplasmatic reticulum acquiring a transient lipid envelope before leaving the infected cell. Capsid/nucleocapsid is round and exhibits icosahedral symmetry. The capsid is isometric and has a diameter of 60-80 nm. The capsid shells of virions are composed of two layers, or three layers. All shells are usually present, or the outer shell is often lost during preparation. Capsids appear round. The capsid surface structure reveals a regular pattern with distinctive features is smooth, or appears rough. The capsomer arrangement is clearly visible. Surface projections are often lost during preparation, or not present, or distinct spikes protruding from the 12 vertices. Virus preparations contain one particle component. Only one species is recovered in preparations. Incomplete particles are common. They are devoid of nucleic acid characterized by capsids with dark centers in negative stain preparations, or incompletely assembled capsids. Physicochemical and Physical Properties Virions have a buoyant density in CsCl of 1.26-1.44 g cm-3. Nucleic Acid The Mr of the genome constitutes 15-20% of the virion by weight. The genome is monomeric; segmented and consists of ten segments of to twelve segments, depending on genus, of linear, double-stranded RNA. The complete genome is 18200-30500 nucleotides long. The 5'-end of the genome has a methylated nucleotide cap (on the positive strand of each duplex, the negative strands have a phosphorylated terminus, cap sequence type is m7G5ppp5'GmpNp. The multipartite genome is found in one type of particle only. Each virion contains a single copy of the genome; a full length copy. Proteins Proteins constitute about 80-85% of the particle weight. The viral genome encodes structural proteins and non-structural proteins. Lipids Lipids are usually absent, or present during morphogenesis in minute amounts as myristic acid residues (covalently attached to one of the virion proteins) and are located in the envelope (in an intermediate stage that is subsequently removed).