Iridoviridae. Iridoviridae

Description of Iridoviridae adapted from ICTVdb Virion Properties Morphology Virions consist of an envelope, a capsid, and an internal lipid membrane. Virus capsid is not enveloped, or enveloped (with a membrane-derived envelope by a double layer envelope. Virions are spherical and measure 160-350 nm in diameter. Internal lipid membrane located between outer and inner protein shell. Capsid/nucleocapsid is round and exhibits icosahedral symmetry. The capsid is isometric and has a diameter of 125-300 nm. Capsids appear hexagonal in outline. The capsid consists of probably 72 capsomers. Surface projections are not prominent, or distinct, numerous filaments, some of which are trailing from the icosahedron. Physicochemical and Physical Properties Virions have a buoyant density in CsCl of 1.26-1.36 g cm-3. Nucleic Acid The Mr of the genome constitutes 12-30% of the virion by weight. The genome is not segmented and contains a single molecule of linear double-stranded DNA. The complete genome is 150000-280000 nucleotides long. The genome has a guanine + cytosine content of 20-58 %. The genome contains unusual bases, they are 5-methyl deoxy-cytosine residues (in some genera). Double stranded DNA is can be circularly permuted (in some genera). The genome has terminally redundant sequences. The terminally redundant sequences have direct terminal repeats. Each virion contains a single copy of the genome to multiple copies of the genome; sometimes 2 copies per particle. Proteins The viral genome encodes structural proteins and non-structural proteins. Lipids Lipids are present and located in the internal component. Virions are composed of 3-14% lipids by weight. The composition of viral lipids is known. The composition of viral lipids and host cell membranes are distinctly different. The lipids are not derived from host membranes.