Iridoviridae
Encyclopedia
Iridoviridae are a family of viruses with double stranded DNA genomes. The name is derived from Iris
the Greek
goddess
of the rainbow
. This name was chosen because of the "rainbow like" iridescence observed in heavily infected insects and pelleted samples of invertebrate iridoviruses.
, Megalocytivirus
and Ranavirus
.
The taxonomy of this family is under revision with molecular methods and may be revised.
The linear genome varies between 150-303 kilobases 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 the Lymphocystivirus, Megalocytivirus and Ranavirus genera have genomes with ~25% of their cytosine
residues methylated by a virally encoded DNA methyltransferase
.
The viral DNA is transported to the host cell nucleus
where it is transcribed by host RNA polymerase
II modified by the virus. Meanwhile host macromolecular synthesis is stopped.
Parental DNA produces a genome which is then the template for replication in the cytoplasm
. Large concatemers of viral DNA are formed by recombination in the cytoplasm.
Packaging of the new genomes into virons occurs in the cytoplasm and the virus is released either by budding from of the cell membrane or cell lysis.
species such as fish, amphibians and reptiles.
Iris (mythology)
In Greek mythology, Iris is the personification of the rainbow and messenger of the gods. As the sun unites Earth and heaven, Iris links the gods to humanity...
the Greek
Greece
Greece , officially the Hellenic Republic , and historically Hellas or the Republic of Greece in English, is a country in southeastern Europe....
goddess
Goddess
A goddess is a female deity. In some cultures goddesses are associated with Earth, motherhood, love, and the household. In other cultures, goddesses also rule over war, death, and destruction as well as healing....
of the rainbow
Rainbow
A rainbow is an optical and meteorological phenomenon that causes a spectrum of light to appear in the sky when the Sun shines on to droplets of moisture in the Earth's atmosphere. It takes the form of a multicoloured arc...
. This name was chosen because of the "rainbow like" iridescence observed in heavily infected insects and pelleted samples of invertebrate iridoviruses.
Taxonomy
The family contains five genera: Chloriridovirus, Iridovirus, LymphocystivirusLymphocystivirus
Lymphocystivirus is one of five genera of viruses within the viral family Iridoviridae, and one of three genera within this family which infect teleost fishes, along with Megalocytivirus and Ranavirus...
, Megalocytivirus
Megalocytivirus
Megalocytivirus is one of five genera of viruses within the family Iridoviridae and one of three genera within this family which infect teleost fishes, along with Lymphocystivirus and Ranavirus. The megalocytiviruses are an emerging group of closely related dsDNA viruses which cause systemic...
and Ranavirus
Ranavirus
Ranavirus is one of five genera of viruses within the family Iridoviridae, one of the five families of nucleocytoplasmic large DNA viruses . Ranavirus is the only genus within Iridoviridae that includes viruses that are infectious to amphibians and reptiles, and one of only three genera within...
.
The taxonomy of this family is under revision with molecular methods and may be revised.
Virology
The virons are icosahedral with triangulation number (T) = 189-217, 120-350 nm in diameter and made up of three domains; an outer proteinaceous capsid, an intermediate lipid 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 (envoloped viruses) or were arranged in paracrystaline array within the host cell cytoplasm and then were released by cell lysis (non enveloped viruses).The linear genome varies between 150-303 kilobases 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 the Lymphocystivirus, Megalocytivirus and Ranavirus genera have genomes with ~25% of their cytosine
Cytosine
Cytosine is one of the four main bases found in DNA and RNA, along with adenine, guanine, and thymine . It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached . The nucleoside of cytosine is cytidine...
residues methylated by a virally encoded DNA methyltransferase
Methyltransferase
A methyltransferase is a type of transferase enzyme that transfers a methyl group from a donor to an acceptor.Methylation often occurs on nucleic bases in DNA or amino acids in protein structures...
.
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
Cell nucleus
In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...
where it is transcribed by host RNA polymerase
RNA polymerase
RNA polymerase is an enzyme that produces RNA. In cells, RNAP is needed for constructing RNA chains from DNA genes as templates, a process called transcription. RNA polymerase enzymes are essential to life and are found in all organisms and many viruses...
II modified by the virus. Meanwhile host macromolecular synthesis is stopped.
Parental DNA produces a genome which is then the template for replication in the cytoplasm
Cytoplasm
The cytoplasm is a small gel-like substance residing between the cell membrane holding all the cell's internal sub-structures , except for the nucleus. All the contents of the cells of prokaryote organisms are contained within the cytoplasm...
. Large concatemers of viral DNA are formed by recombination in the cytoplasm.
Packaging of the new genomes into virons occurs in the cytoplasm and the virus is released either by budding from of the cell membrane or cell lysis.
Pathogenesis
Little is known about the pathogenesis 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, but also some vertebrateVertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
species such as fish, amphibians and reptiles.