|Group:||Group I (dsDNA)|
Phycodnaviruses (members of the family Phycodnaviridae) are large (160 to 560 thousand base pairs), double stranded DNA viruses that infect marine or freshwater eukaryotic algae. They belong to a super-group of large viruses known as nucleocytoplasmic large DNA viruses (NCLDVs).
Phycodnaviruses have icosahedral morphology, an internal lipid membrane and replicate, completely or partly, in the cytoplasm of their host cells. The genomes range in size from 100 kilobases (kb) to >550 kb with G+C content between 40% and 50%.
The taxonomy of this family was initially based on the host range: Chlorovirus infect chlorella-like green algae from terrestrial waters, whereas members of the other five genera (Coccolithovirus, Phaeovirus, Prasinovirus, Prymnesiovirus and Raphidovirus) infect marine green and brown algae. This was subsequently confirmed by analysis of their DNA polymerases.
Recent studies have revealed features in Phycodnavirus genomes such as sophisticated replication and transcription machineries, a novel type of potassium channel protein, genes involved in inducing apoptosis in the host genome, a sophisticated signal transduction and gene regulation system and genes for glycosylation of viral proteins.
All of the Phycodnaviruses encode a number of proteins involved in DNA replication or recombination, including a DNA-directed DNA polymerase. It is unclear if any of the Phycodnaviruses encode a fully functional replication machinery, however. They are thought to rely on host enzymes at least partially.
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