Description of Phycodnaviridae
adapted from
ICTVdb
Virion Properties
Morphology
Virions consist of a
capsid. Virus capsid is not enveloped. Virion attaches to host
cell surface and releases DNA into the host cell in a similar
fashion as
Tectiviridae. Capsid/nucleocapsid is round and
exhibits polyhedral symmetry. The isometric capsid has a diameter
of 130-200 nm. The capsid shells of virions are composed of
multiple layers (multilaminated capsid). Capsids appear hexagonal
in outline.
Physicochemical and Physical Properties
Virions have a buoyant density in
CsCl of 1.25-1.3 g cm
-3.
Nucleic Acid
The Mr of the genome constitutes 21-25% of the
virion by weight. The genome is not segmented and contains a
single molecule of linear double-stranded DNA. The complete
genome is 250000-350000 nucleotides long. The genome has a
guanine + cytosine content of 40-52 %. The genome contains
unusual bases (varying from 0.1-47 %), they are 5-methyl
deoxy-cytosine residues and N6-methyl deoxy-adenosine residues
(in some DNAs). Double stranded DNA is non-permuted; the genome
sequence has termini with cross-linked hairpin ends. The genome
minus the hairpin has terminally redundant sequences. The
terminally redundant sequences have inverted terminal repetitions
(ITR) (for at least 2000 bases).
Proteins
Proteins constitute about 64% of the
particle weight.
The viral genome encodes structural proteins and
non-structural proteins.
Lipids
Lipids are present and located in the
internal component (located inside the glycoprotein shell).
Virions are composed of 5-10% lipids by weight (beneath the outer
glycoprotein shell). Lipids are essential for infectivity.