''Cypovirus'', short for cytoplasmic polyhedrosis virus, is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

double-stranded RNA viruses Double-stranded RNA viruses (dsRNA viruses) are a polyphyletic group of viruses 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 pol ...

in 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-layered ...

'' and subfamily ''

Spinareovirinae ''Spinareovirinae'' is a subfamily of double-stranded RNA viruses in the family ''Reoviridae''. Viruses in this group are distinguished by the presence of a turreted protein on the inner capsid. (''Spina'' = spiny or thorny in Latin.) Taxonomy ...

''. Cypoviruses have only been isolated from

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pairs ...

s. Diseases associated with this genus include chronic

diarrhoea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration often begin wi ...

and pale blue iridescence in the guts of larvae. Sixteen species are placed in this genus. Cypoviruses structurally have muc in common with the more widely studied

nucleopolyhedrovirus ''Alphabaculovirus'' is a genus of viruses in the family ''Baculoviridae''. The natural hosts of species in this family are invertebrates, among them winged insects ( Lepidopterans, Hymenopterans, Dipterans), and decapods. However, species i ...

es, a genus of arthropod viruses in the family ''

Baculoviridae ''Baculoviridae'' is a family of viruses. Arthropods, among the most studied being Lepidoptera, Hymenoptera and Diptera, serve as natural hosts. Currently, 85 species are placed in this family, assigned to four genera. Baculoviruses are known ...

''. However, cypoviruses have an RNA genome and replicate in the cytoplasm of the infected cells, while nucleopolyhedroviruses have a DNA genome and replicate in the nucleus.

Structure

Viruses in the genus ''Cypovirus'' are

nonenveloped A viral envelope is the outermost layer of many types of viruses. It protects the genetic material in their life cycle when traveling between host cells. Not all viruses have envelopes. Numerous human pathogenic viruses in circulation are encase ...

, with icosahedral geometries, and T=2 symmetry. Cypoviruses have only a single

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 may ...

shell, which is similar to 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 respirato ...

inner core. They exhibit striking capsid stability, which is fully capable of endogenous RNA transcription and processing. The capsid diameter is around 65 nm.

Genome

Genomes are linear and segmented. The genome codes for 10 to 12 proteins. Classification of cypoviruses is based on the

electrophoretic Electrophoresis, from Ancient Greek ἤλεκτρον (ḗlektron, "amber") and φόρησις (phórēsis, "the act of bearing"), is the motion of dispersed particles relative to a fluid under the influence of a spatially uniform electric fi ...

migration profiles of their genome segments. The overall folds of cypovirus proteins are similar to those of other reoviruses, but they have insertional domains and unique structures that contribute to their extensive intermolecular interactions. The cypovirus 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 helices, ...

-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.

Lifecycle

Viral replication is cytoplasmic. Entry into the host cell is achieved by attachment to host receptors, which mediates endocytosis. Replication follows the double-stranded RNA virus replication model. Double-stranded RNA virus transcription is the method of transcription. Translation takes place by ribosomal skipping. The virus exits the host cell by monopartite nontubule guided viral movement, and exists in occlusion bodies after cell death and remains infectious until finding another host. Insects serve as their natural hosts. Transmission routes are fecal-oral, parental, and egg transmission. Infection occurs when a susceptible insect consumes viral polyhedra, usually as a contaminant on the insect’s food (in most cases, foliage of a plant). The polyhedra dissolve in the digestive tract of the insect, releasing the virus particles that penetrate the gut epithelial cells. Replication of the virus is often confined to these cells and the progeny virus, in the form of new polyhedra are excreted in the insect feces, thus contaminating more foliage resulting in the spread of the disease to additional insects. The progression of the disease can be rather slow, but the virus infection is normally fatal.

Species

The genus ''Cypovirus'' consists of 16 accepted species: ''

Cypovirus 1 ''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 ...

'' through ''

Cypovirus 16 ''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 ge ...

''.

References

External links