| Iridoviridae | |
|---|---|
 | |
| TEM micrograph showing a cluster ofIridovirus virions | |
Virus classification | |
| (unranked): | Virus |
| Realm: | Varidnaviria |
| Kingdom: | Bamfordvirae |
| Phylum: | Nucleocytoviricota |
| Class: | Megaviricetes |
| Order: | Pimascovirales |
| Family: | Iridoviridae |
| Subfamilies and genera | |
See text | |
Iridoviridae is a family ofviruses with double-strandedDNA genomes.[1] Amphibians, fish, and invertebrates such as arthropods serve as natural hosts. There are currently 22 species in this family, divided among two subfamilies and seven genera.[1][2]
The name is derived fromIris, theGreekgoddess of therainbow. This name was chosen because of the "rainbow-like" iridescence observed in heavily infected insects and pelleted samples ofinvertebrate iridoviruses.[3]
The following subfamilies and genera are recognized (-virinae denotes subfamily and -virus denotes genus):[4]
Thevirions areicosahedral withtriangulation number (T) = 189–217, 120–350 nm in diameter and made up of three domains: an outer proteinaceouscapsid, an intermediatelipid membrane, and a central core containing DNA-protein complexes. Some of the viruses also have an outer envelope. The presence or absence of an envelope depends on whether they budded from thecell membrane (enveloped viruses) or were arranged inparacrystalline arrays within the host cellcytoplasm and then were released bycell lysis (unenveloped viruses).[citation needed]
The linear genome varies between 150 and 303kilobases in length. It contains terminal and redundant sequences and is circularly permuted.[citation needed]
Members of this family differ in their degree of genomemethylation. The generaChloriridovirus andIridovirus lack a highly methylated genome. Members ofLymphocystivirus,Megalocytivirus, andRanavirus have genomes with about 25% of theircytosine residues methylated by a virally encoded DNAmethyltransferase.[citation needed]
| Genus | Structure | Symmetry | Genomic arrangement | Genomic segmentation |
|---|---|---|---|---|
| Lymphocystivirus | Polyhedral | T=189–217 | Linear | Monopartite |
| Megalocytivirus | Polyhedral | T=189–217 | Linear | Monopartite |
| Ranavirus | Polyhedral | T=133 or 147 | Linear | Monopartite |
| Iridovirus | Polyhedral | T=147 | Linear | Monopartite |
| Chloriridovirus | Polyhedral | T=189–217 | Linear | Monopartite |
Similar to theherpes viruses, transcription occurs in three stages: immediate-early, delayed-early, and late. Positive induction and negative feedback mechanisms exist in each stage, mediated by products of the other stages.[citation needed]
Virus particles enter the cell and uncoating occurs. The viral DNA is transported to the hostcell nucleus, where it is transcribed by hostRNA polymerase II modified by the virus. Meanwhile, host macromolecular synthesis ceases.
Parental DNA produces a genome which is then the template for replication in thecytoplasm. Largeconcatemers of viral DNA are formed by recombination in the cytoplasm. Packaging of the new genomes into virions occurs in the cytoplasm and the virus is released either by budding from the cell membrane or cell lysis.
| Genus | Host details | Tissue tropism | Entry details | Release details | Replication site | Assembly site | Transmission |
|---|---|---|---|---|---|---|---|
| Lymphocystivirus | Fish | None | Cell receptor endocytosis | Lysis; budding | Nucleus | Cytoplasm | Unknown |
| Megalocytivirus | Fish | None | Cell receptor endocytosis | Lysis; budding | Nucleus | Cytoplasm | Unknown |
| Ranavirus | Frogs; snakes | None | Cell receptor endocytosis | Lysis; budding | Nucleus | Cytoplasm | Contact |
| Iridovirus | Insects | None | Cell receptor endocytosis | Lysis; budding | Nucleus | Cytoplasm | Contact |
| Chloriridovirus | Diptera with aquatic larval stage, mainly mosquitoes | None | Cell receptor endocytosis | Budding | Nucleus | Cytoplasm | Unknown |
Members of theIridoviridae appear to have the capability to repairDNA damages.[5]
Little is known about thepathogenesis of iridoviruses. The pathogenesis is, however, temperature dependent and iridoviruses are thus confined topoikilothermic hosts.[citation needed]
Members of theIridoviridae family infect mainlyinvertebrates, but also somevertebrate species such as fish, amphibians and reptiles.[citation needed]
MicrobiologyBytes: Iridoviruses, archived fromthe original on February 24, 2007, retrieved2007-03-06Viral Bioinformatics Resource Center & Viral Bioinformatics – Canada, University of Victoria, archived fromthe original on August 17, 2007, retrieved2007-03-06
