Double-stranded RNA viruses (dsRNA viruses) are a

polyphyletic A polyphyletic group is an assemblage of organisms or other evolving elements that is of mixed evolutionary origin. The term is often applied to groups that share similar features known as homoplasies, which are explained as a result of conver ...

group of

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

es that have double-stranded genomes made of ribonucleic acid. The double-stranded genome is used to transcribe a positive-strand RNA by the viral RNA-dependent RNA polymerase (RdRp). The positive-strand RNA may be used as messenger RNA (mRNA) which can be translated into viral proteins by the host cell's ribosomes. The positive-strand RNA can also be replicated by the RdRp to create a new double-stranded viral genome. Double-stranded RNA viruses are classified in two separate phyla ''

Duplornaviricota ''Duplornaviricota'' is a phylum of RNA viruses, which contains all double-stranded RNA viruses, except for those in phylum '' Pisuviricota.'' Characteristic of the group is a viral capsid composed of 60 homo- or heterodimers of capsid protein on ...

'' and ''

Pisuviricota ''Pisuviricota'' is a phylum of RNA viruses that includes all positive-strand and double-stranded RNA viruses that infect eukaryotes and are not members of the phylum '' Kitrinoviricota,'' ''Lenarviricota'' or '' Duplornaviricota.'' The name of ...

'' (specifically class ''

Duplopiviricetes ''Durnavirales'' is an order of double-stranded RNA viruses which infect eukaryotes. The name of the group derives from Italian ''duplo'' which means double (a reference to double-stranded), ''rna'' for the type of virus, and -''virales'' which i ...

''), which are in the kingdom '' Orthornavirae'' and realm '' Riboviria''. The two groups do not share a common dsRNA virus ancestor. Double-stranded RNA viruses evolved two separate times from

positive-strand RNA virus Positive-strand RNA viruses (+ssRNA viruses) are a group of related viruses that have positive-sense, single-stranded genomes made of ribonucleic acid. The positive-sense genome can act as messenger RNA (mRNA) and can be directly translated int ...

es. In the

Baltimore classification Baltimore classification is a system used to classify viruses based on their manner of messenger RNA (mRNA) synthesis. By organizing viruses based on their manner of mRNA production, it is possible to study viruses that behave similarly as a d ...

system, dsRNA viruses belong to Group III. Virus group members vary widely in host range (

animal Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...

plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclu ...

fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...

, and

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...

), genome segment number (one to twelve), and

virion A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsky's ...

organization ( T-number,

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 ma ...

layers, or turrets). Double-stranded RNA viruses include the

rotavirus ''Rotavirus'' is a genus of double-stranded RNA viruses in the family ''Reoviridae''. Rotaviruses are the most common cause of diarrhoeal disease among infants and young children. Nearly every child in the world is infected with a rotavirus ...

es, known globally as a common cause of gastroenteritis in young children, and bluetongue virus, an economically significant pathogen of cattle and sheep. The family ''

Reoviridae ''Reoviridae'' is a family of double-stranded RNA viruses. Member viruses have a wide host range, including vertebrates, invertebrates, plants, protists and fungi. They lack lipid envelopes and package their segmented genome within multi-layere ...

'' is the largest and most diverse dsRNA virus family in terms of host range.

Classification

Two clades of dsRNA viruses exist: the phylum ''Duplornaviricota'' and the class ''Duplopiviricetes'', which is in the phylum ''Pisuviricota''. Both are included in the kingdom ''Orthornavirae'' in the realm ''Riboviria''. Based on phylogenetic analysis of RdRp, the two clades do not share a common dsRNA ancestor but are instead separately descended from different positive-sense, single-stranded RNA viruses. In the

system, which groups viruses together based on their manner of mRNA synthesis, dsRNA viruses are group III.

''Duplornaviricota''

'' contains most dsRNA viruses, including reoviruses, which infect a diverse range of eukaryotes, and cystoviruses, which are the only dsRNA viruses known to infect prokaryotes. Apart from RdRp, viruses in ''Duplornaviricota'' also share icosahedral capsids that contain 60 homo- or heterodimers of the capsid protein organized on a pseudo T=2 lattice. The phylum is divided into three classes: '' Chrymotiviricetes'', which primarily contains fungal and protozoan viruses, ''Resentoviricetes'', which contains reoviruses, and ''Vidaverviricetes'', which contains cystoviruses.

''Duplopiviricetes''

The class ''

'' is the second clade of dsRNA viruses and is in the phylum ''

'', which also contains positive-sense single-stranded RNA viruses. ''Duplopiviricetes'' mostly contains plant and fungal viruses and includes the following four families: '' Amalgaviridae'', '' Hypoviridae'', '' Partitiviridae'', and '' Picobirnaviridae''.

Notes on selected species

Reoviridae

'' are currently classified into nine genera. The genomes of these viruses consist of 10 to 12 segments of dsRNA, each generally encoding one

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...

. The mature virions are non-enveloped. Their capsids, formed by multiple proteins, have

icosahedral In geometry, an icosahedron ( or ) is a polyhedron with 20 faces. The name comes and . The plural can be either "icosahedra" () or "icosahedrons". There are infinitely many non- similar shapes of icosahedra, some of them being more symmetrica ...

symmetry and are arranged generally in concentric layers. A distinguishing feature of the dsRNA viruses, irrespective of their family association, is their ability to carry out

transcription Transcription refers to the process of converting sounds (voice, music etc.) into letters or musical notes, or producing a copy of something in another medium, including: Genetics * Transcription (biology), the copying of DNA into RNA, the fir ...

of the dsRNA segments, under appropriate conditions, within the capsid. In all these viruses, the

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...

s required for endogenous transcription are thus part of the virion structure.

Orthoreoviruses

The

orthoreovirus ''Orthoreovirus'' is a genus of viruses, in the family ''Reoviridae'', in the subfamily '' Spinareovirinae''. Vertebrates serve as natural hosts. There are ten species in this genus. Diseases associated with this genus include mild upper respirat ...

es (

reovirus ''Reoviridae'' is a family of double-stranded RNA viruses. Member viruses have a wide host range, including vertebrates, invertebrates, plants, protists and fungi. They lack lipid envelopes and package their segmented genome within multi-layered ...

es) are the prototypic members of the virus ''

'' family and representative of the turreted members, which comprise about half the genera. Like other members of the family, the reoviruses are non-enveloped and characterized by concentric capsid shells that encapsidate a segmented dsRNA

genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding g ...

. In particular, reovirus has eight structural proteins and ten segments of dsRNA. A series of uncoating steps and conformational changes accompany cell entry and replication. High-resolution structures are known for almost all of the proteins of mammalian reovirus (MRV), which is the best-studied genotype. Electron cryo- microscopy (cryoEM) and X-ray crystallography have provided a wealth of structural information about two specific MRV strains, type 1 Lang (T1L) and type 3 Dearing (T3D).

Cypovirus

The cytoplasmic polyhedrosis viruses (CPVs) form the genus

Cypovirus ''Cypovirus'', short for cytoplasmic polyhedrosis virus, is a genus of double-stranded RNA viruses in the family ''Reoviridae'' and subfamily '' Spinareovirinae''. Cypoviruses have only been isolated from insects. Diseases associated with this g ...

of the family ''

''. CPVs are classified into 14 species based on the electrophoretic migration profiles of their genome segments. Cypovirus has only a single capsid shell, which is similar to the orthoreovirus inner core. CPV exhibits striking capsid stability and is fully capable of endogenous RNA transcription and processing. The overall folds of CPV proteins are similar to those of other reoviruses. However, CPV proteins have insertional domains and unique structures that contribute to their extensive intermolecular interactions. The CPV turret protein contains two

methylase Methyltransferases are a large group of enzymes that all methylate their substrates but can be split into several subclasses based on their structural features. The most common class of methyltransferases is class I, all of which contain a Rossm ...

domains with a highly conserved

helix A helix () is a shape like a corkscrew or spiral staircase. It is a type of smooth space curve with tangent lines at a constant angle to a fixed axis. Helices are important in biology, as the DNA molecule is formed as two intertwined helic ...

-pair/β-sheet/helix-pair sandwich fold but lacks the β-barrel flap present in orthoreovirus λ2. The stacking of turret protein functional domains and the presence of constrictions and A spikes along the mRNA release pathway indicate a mechanism that uses pores and channels to regulate the highly coordinated steps of RNA transcription, processing, and release.

Rotavirus

Rotavirus ''Rotavirus'' is a genus of double-stranded RNA viruses in the family ''Reoviridae''. Rotaviruses are the most common cause of diarrhoeal disease among infants and young children. Nearly every child in the world is infected with a rotavirus ...

is the most common cause of acute gastroenteritis in infants and young children worldwide. This virus contains a dsRNA genome and is a member of the ''

'' family. The genome of rotavirus consists of eleven segments of dsRNA. Each genome segment codes for one protein with the exception of segment 11, which codes for two proteins. Among the twelve proteins, six are structural and six are non-structural proteins. It is a double-stranded RNA non-enveloped virus

Bluetongue virus

The members of genus ''

Orbivirus ''Orbivirus'' is a genus of double-stranded RNA viruses in the family ''Reoviridae'' and subfamily '' Sedoreovirinae''. Unlike other reoviruses, orbiviruses are arboviruses. They can infect and replicate within a wide range of arthropod and ver ...

'' within the ''

'' family are arthropod borne viruses and are responsible for high morbidity and mortality in

ruminant Ruminants (suborder Ruminantia) are hoofed herbivorous grazing or browsing mammals that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microbial actions. The ...

s. Bluetongue virus (BTV) which causes disease in livestock (

sheep Sheep or domestic sheep (''Ovis aries'') are domesticated, ruminant mammals typically kept as livestock. Although the term ''sheep'' can apply to other species in the genus '' Ovis'', in everyday usage it almost always refers to domesticated ...

goat The goat or domestic goat (''Capra hircus'') is a domesticated species of goat-antelope typically kept as livestock. It was domesticated from the wild goat (''C. aegagrus'') of Southwest Asia and Eastern Europe. The goat is a member of the a ...

cattle Cattle (''Bos taurus'') are large, domesticated, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus ''Bos''. Adult females are referred to as cows and adult ma ...

) has been in the forefront of molecular studies for the last three decades and now represents the best understood

orbivirus ''Orbivirus'' is a genus of double-stranded RNA viruses in the family ''Reoviridae'' and subfamily '' Sedoreovirinae''. Unlike other reoviruses, orbiviruses are arboviruses. They can infect and replicate within a wide range of arthropod and ver ...

at the molecular and structural levels. BTV, like other members of the family, is a complex non-enveloped virus with seven structural proteins and a RNA genome consisting of 10 variously sized dsRNA segments.

Phytoreoviruses

Phytoreovirus ''Phytoreovirus'' is a genus of viruses, in the family ''Reoviridae'', in the subfamily ''Sedoreovirinae''. They are non-turreted reoviruses that are major agricultural pathogens, particularly in Asia. Oryza sativa for RDV and RGDV, dicotyledono ...

es are non-turreted reoviruses that are major agricultural pathogens, particularly in Asia. One member of this family,

Rice Dwarf Virus Rice dwarf virus (RDV) is a plant pathogenic virus of the family Reoviridae ''Reoviridae'' is a family of double-stranded RNA viruses. Member viruses have a wide host range, including vertebrates, invertebrates, plants, protists and fungi. T ...

(RDV), has been extensively studied by electron cryomicroscopy and

x-ray crystallography X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...

. From these analyses, atomic models of the capsid proteins and a plausible model for capsid assembly have been derived. While the structural proteins of RDV share no sequence similarity to other proteins, their folds and the overall capsid structure are similar to those of other ''Reoviridae''.

''Saccharomyces cerevisiae'' virus L-A

The L-A dsRNA virus of the

yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constit ...

Saccharomyces cerevisiae ''Saccharomyces cerevisiae'' () (brewer's yeast or baker's yeast) is a species of yeast (single-celled fungus microorganisms). The species has been instrumental in winemaking, baking, and brewing since ancient times. It is believed to have b ...

'' has a single 4.6 kb genomic segment that encodes its major coat protein, Gag (76 kDa) and a Gag-Pol fusion protein (180 kDa) formed by a -1 ribosomal frameshift. L-A can support the replication and

encapsidation {{Short pages monitor