''Iridoviridae'' is a family of

virus A virus is a submicroscopic infectious agent that replicates only inside the living Cell (biology), cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Viruses are ...

es with double-stranded

DNA Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...

genomes. 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.

Nomenclature

The name is derived from Iris, the Greek

goddess A goddess is a female deity. In some faiths, a sacred female figure holds a central place in religious prayer and worship. For example, Shaktism (one of the three major Hinduism, Hindu sects), holds that the ultimate deity, the source of all re ...

of the

rainbow A rainbow is an optical phenomenon caused by refraction, internal reflection and dispersion of light in water droplets resulting in a continuous spectrum of light appearing in the sky. The rainbow takes the form of a multicoloured circular ...

. This name was chosen because of the "rainbow-like" iridescence observed in heavily infected insects and pelleted samples of

invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...

iridoviruses.

Taxonomy

The following subfamilies and genera are recognized (-''virinae'' denotes subfamily and -''virus'' denotes genus): * '' Alphairdovirinae'' ** '' Lymphocystivirus'' ** '' Megalocytivirus'' ** '' Ranavirus'' * '' Betairidovirinae'' ** '' Chloriridovirus'' ** '' Daphniairidovirus'' ** '' Decapodiridovirus'' ** '' Iridovirus''

Structure

The

virion A virion (plural, ''viria'' or ''virions'') is an inert virus particle capable of invading a Cell (biology), cell. Upon entering the cell, the virion disassembles and the genetic material from the virus takes control of the cell infrastructure, t ...

s are icosahedral with triangulation number (T) = 189–217, 120–350 nm in diameter and made up of three domains: an outer proteinaceous

capsid A capsid is the protein shell of a virus, enclosing its genetic material. It consists of several oligomeric (repeating) structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or m ...

, an intermediate

lipid Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include storing ...

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 the

cell membrane The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of a cell from the outside environment (the extr ...

(enveloped viruses) or were arranged in paracrystalline arrays within the host cell

cytoplasm The cytoplasm describes all the material within a eukaryotic or prokaryotic cell, enclosed by the cell membrane, including the organelles and excluding the nucleus in eukaryotic cells. The material inside the nucleus of a eukaryotic cell a ...

and then were released by cell lysis (unenveloped viruses). The linear genome varies between 150 and 303

kilobase A base pair (bp) is a fundamental unit of double-stranded nucleic acids consisting of two nucleobases bound to each other by hydrogen bonds. They form the building blocks of the DNA double helix and contribute to the folded structure of both DNA ...

s in length. It contains terminal and redundant sequences and is circularly permuted. Members of this family differ in their degree of genome methylation. The genera ''Chloriridovirus'' and ''Iridovirus'' lack a highly methylated genome. Members of ''Lymphocystivirus'', ''Megalocytivirus'', and ''Ranavirus'' have genomes with about 25% of their

cytosine Cytosine () (symbol C or Cyt) is one of the four nucleotide bases found in DNA and RNA, along with adenine, guanine, and thymine ( uracil in RNA). It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attac ...

residues methylated by a virally encoded DNA methyltransferase.

Gene expression

Similar to the herpes 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.

Replication

Virus particles enter the cell and uncoating occurs. The viral DNA is transported to the host

cell nucleus The cell nucleus (; : nuclei) is a membrane-bound organelle found in eukaryote, eukaryotic cell (biology), cells. Eukaryotic cells usually have a single nucleus, but a few cell types, such as mammalian red blood cells, have #Anucleated_cells, ...

, where it is transcribed by host

RNA polymerase In molecular biology, RNA polymerase (abbreviated RNAP or RNApol), or more specifically DNA-directed/dependent RNA polymerase (DdRP), is an enzyme that catalyzes the chemical reactions that synthesize RNA from a DNA template. Using the e ...

II modified by the virus. Meanwhile, host macromolecular synthesis ceases. Parental DNA produces a genome which is then the template for replication in the

. Large concatemers 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.

DNA repair

Members of the ''Iridoviridae'' appear to have the capability to repair DNA damages.Ke F, Zhang QY. ADRV 12L: A Ranaviral Putative Rad2 Family Protein Involved in DNA Recombination and Repair. Viruses. 2022 Apr 27;14(5):908. doi: 10.3390/v14050908. PMID 35632650; PMCID: PMC9146916

Pathogenesis

Little is known about the

pathogen In biology, a pathogen (, "suffering", "passion" and , "producer of"), in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a Germ theory of d ...

esis of iridoviruses. The pathogenesis is, however, temperature dependent and iridoviruses are thus confined to poikilothermic hosts.

Host range

Members of the ''Iridoviridae'' family infect mainly

invertebrates Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordate subphylum ...

, but also some

vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

species such as fish, amphibians and reptiles.

References

External links

ICTV Online (10th) Report: ''Iridoviridae''

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