Phycodnaviridae. Phycodnaviridae

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.