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.