Reoviridae

Structure of the reovirus virion

Reoviruses are non-enveloped and have an icosahedral capsid composed of an outer (T=13) and inner (T=2) protein shell.[1][5] Ultrastructural studies shows that virion capsids composed of two or tree separate layers which depend their type. The innermost layer(core) has T=1 icosahedral symmetry and composed of 60 different type of structural proteins. The core contains genom segments, each of them encode variety enzyme structure which is required for transcription. The core is covered by capsid layer T=13 icosahedral symmetry. Reovirus has unique structure which is contain glycolisated spike protein on the surface. [8]The genomes of viruses in Reoviridae contain 10–12 segments which are grouped into three categories corresponding to their size: L (large), M (medium) and S (small). Segments range from about 0.2 to 3 kbp and each segment encodes 1–3 proteins (10–14 proteins in total[1]). Proteins of viruses in the Reoviridae are denoted by the Greek character corresponding to the segment it was translated from (the L segment encodes for λ proteins, the M segment encodes for μ proteins and the S segment encodes for σ proteins).[5]

Viruses in the family Reoviridae have genomes consisting of segmented, double-stranded RNA (dsRNA).[4] Because of this, replication occurs exclusively in the cytoplasm and the virus encodes several proteins which are needed for replication and conversion of the dsRNA genome into (+)-RNAs. The virus can enter the host cell via a receptor on the cell surface. The receptor is not known but is thought to include sialic acid and junctional adhesion molecules (JAMs).[9] The virus is partially uncoated by proteases in the endolysosome, where the capsid is partially digested to allow further cell entry. The core particle then enters the cytoplasm by a yet unknown process where the genome is transcribed conservatively causing an excess of (+) sense strands, which are used as mRNA templates to synthesize (−) sense strands. The genome of rotavirus is separated via 11 segmented as mentioned before. These 11 segmented genome associated with VP1 molecule which responsible for RNA synthesizes. In early events the selection process is occurred to allow the entry of 11 different RNA species in the cell. This procedure is performed by newly synthesized RNAs. This event ensures to receives one each of the 11 different RNA species. In late events transcription process is occurred again but this time are not capped unlikely early events. For virus different amounts of RNAs are required therefore in translation step there is a control machinery. There are same quantities RNAs but different quantities of proteins. The reason of this, RNAs are not translated same rate.[10]

Viral particles begin to assemble in the cytoplasm 6–7 hours after infection. Translation takes place by leaky scanning, suppression of termination, and ribosomal skipping. The virus exits the host cell by monopartite non-tubule guided viral movement, cell to cell movement, and existing in occlusion bodies after cell death and remaining infectious until finding another host.[1]

Multiplicity reactivation (MR) is the process by which two or more virus genomes, each containing inactivating genome damage, can interact within an infected cell to form a viable virus genome. McClain and Spendlove[11] demonstrated MR for three types of reovirus after exposure to ultraviolet irradiation. In their experiments, reovirus particles were exposed to doses of UV-light that would be lethal in single infections. However, when two or more inactivated viruses were allowed to infect individual host cells MR occurred and viable progeny were produced. As they stated, multiplicity reactivation by definition involves some type of repair. Michod et al.[12] reviewed numerous examples of MR in different viruses, and suggested that MR is a common form of sexual interaction in viruses that provides the benefit of recombinational repair of genome damages.

Group: dsRNA

[3]

The Reoviridae are divided into two subfamilies[13] based on the presence of a "turret" protein on the inner capsid.[14][15] From ICTV communications: "The name Spinareovirinae will be used to identify the subfamily containing the spiked or turreted viruses and is derived from 'reovirus' and the Latin word 'spina' as a prefix, which means spike, denoting the presence of spikes or turrets on the surface of the core particles. The term 'spiked' is an alternative to 'turreted', that was used in early research to describe the structure of the particle, particularly with the cypoviruses. The name Sedoreovirinae will be used to identify the subfamily containing the non-turreted virus genera and is derived from 'reovirus' and the Latin word 'sedo', which means smooth, denoting the absence of spikes or turrets from the core particles of these viruses, which have a relatively smooth morphology."[16]

Phylogenetic comparison of the viral polymerase protein sequences of viruses of the family Reoviridae. Arrow indicates a common phylogenetic origin between seadornaviruses and rotaviruses.

Although reoviruses are mostly nonpathogenic in humans, these viruses have served as very productive experimental models for studies of viral pathogenesis.[19] Newborn mice are exquisitely sensitive to reovirus infection and have been used as the preferred experimental system for studies of reovirus pathogenesis.[20]

The reoviruses have been demonstrated to have oncolytic (cancer-killing) properties, encouraging the development of reovirus-based therapies for cancer treatment.[21][22]

Reolysin is a formulation of reovirus (reovirus serotype 3-dearing strain[23]) that is currently in clinical trials for the treatment of various cancers,[24] including studies currently developed to investigate the role of Reolysin combined with other immunotherapies.[23]

• Double-stranded RNA viruses
• Oncolytic virus
• Orphan virus

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• Viralzone: Reoviridae
• ICTV: Reoviridae
• Description of plant viruses: Reoviridae
• ViPR: Reoviridae
• "Reoviridae". NCBI Taxonomy Browser. 10880.