-end of the viral RNA is polyadenylated and in most species there is a protein, VPg, covalently linked to the 5-end of the genome.
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Type Species |
(CrPV) |
Virions are roughly spherical with a particle diameter of approximately 30 nm and no envelope. The virions exhibit icosahedral symmetry (T = 3), (Fig. 1).
Physicochemical and Physical Properties
Virions have a buoyant density in CsCl of between 1.34 and 1.37g/cm3 and sedimentation coefficients of between 153 and 167S. For those species where physicochemical stability has been assessed (CrPV) the virions are stable at pH 3.0.
Particles contain a single molecule of linear, positive sense, ssRNA of 9-10 kb in size. The 3-end of the viral RNA is polyadenylated and in most species there is a protein, VPg, covalently linked to the 5-end of the genome.
Mature virions contain three major structural proteins with Mr of 28-37 
103. In some species a fourth smaller structural protein (Mr = 4.5-9 103) has been reported. In most species a minor structural component - larger than the major capsid proteins (CPs) - has also been reported and is presumed to be the precursor of one of the major structural proteins.
None reported.
None reported.
Genome Organization and Replication
The genome consists of ssRNA with a 5 untranslated region of 500-800 nts followed by two ORFs of around 5,500 and 2,600 nts separated by an untranslated region of approximately 190 nts (Fig. 2). The CPs have been shown by direct sequence analysis to be encoded by the ORF proximal to the 3-end. The 5 ORF encodes protein(s) with sequence motifs related to the helicase, protease and replicase domains of other positive sense RNA viruses of plants and animals e.g., picornaviruses, comoviruses and sequiviruses.
The mechanism of virus entry into cells is unknown. Initiation of protein synthesis coincides with shutdown or down-regulation of host cell protein synthesis. Large precursor proteins are produced in infected cells which are then cleaved to produce an array of smaller polypeptides.
In the case of CrPV and Drosophila C virus (DCV) the structural proteins have been found to be synthesized in supramolar excess relative to the non-structural proteins. No subgenomic messenger RNA is produced during the infection. It is unclear exactly how translation of ORF2 is initiated but for Plautia stali intestine virus (PSIV) in vitro studies using a rabbit reticulocyte translation system have shown that the intervening region between ORFs 1 and 2 can direct initiation of translation.
Virions are assembled in the cytoplasm of the cells and tend to form large paracrystalline arrays with most member species.
All species are serologically distinct. However, there is some serological relatedness between CrPV and DCV which shows a reaction of partial identity in agar double diffusion test with some sera raised against CrPV.
All members of the genus have been isolated from invertebrate species. CrPV has come from species of Orthoptera, Hymenoptera, Lepidoptera, Hemiptera and Diptera. DCV have come only from Diptera species while HiPV, PSIV and RhPV have only come from hemipteran species. Transmission can be by horizontal (per os) or vertical routes. No vectors are known to be involved in transmission.
CrPV is known to have a wide host range and to be widely distributed in nature. DCV is commonly associated with Drosophila species both in nature and in laboratory cultures. Infections with most viruses are usually not associated with a noticeable disease state although they commonly lead to reduced life-expectancy of infected individuals. Under some circumstances CrPV shows increased tropism for neural cells and can lead to an obvious paralytic disease state.
CrPV and DCV replicate readily in several established Drosophila cell lines. CrPV has also been found to replicate in a number of other established insect cell lines. There are no cell lines known that are able to support replication of the other members.
List of Species Demarcation Criteria in the Genus
The list of species demarcation criteria is:
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Natural host range: Species can also be differentiated on the basis of their natural host range and their relative ability to replicate in a range of cultured insect cells. |
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Serology: All species are serologically distinct. |
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Sequence identity between the CPs of isolates and strains of a species is above 90%. |
Official virus species names are in italics. Tentative virus species names, alternative names ( ), strains or serotypes are not italicized. Virus names, genome sequence accession numbers [ ], and assigned abbreviations ( ) are:
|
Cricket paralysis virus |
[M21938] |
(CrPV) |
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Drosophila C virus |
[AF014388] |
(DCV) |
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Himetobi P virus |
[AB017037] |
(HiPV) |
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Plautia stali intestine virus |
[AB006531] |
(PSIV) |
|
Rhopalosiphum padi virus |
[AF022937] |
(RhPV) |
Tentative Species in the Genus
None reported.
Phylogenetic Relationships within the Genus
Members of the “CrPV-like viruses” genus have some similarities to the picornaviruses and to the other families within the picornavirus superfamily (Comoviridae Picornaviridae, Potyviridae, and Sequiviridae). For instance, the gene order of the nonstructural proteins is the same as for members of the picornavirus superfamily i.e., H-P-Rep. Like the other isometric members of the superfamily for which the structure is known, CrPV shows the same, pseudo T = 3 symmetry. However, unlike viruses in the picornavirus superfamily, the genomic RNA of members of the “CrPV-like viruses” genus do not act as an exclusive message for a single polyprotein with all proteins being produced as the results of processing.
There are over 20 RNA-containing viruses of approximately 30 nm in diameter that have been described from insects for which the taxonomic status is not known. Many of these have characteristics that are superficially similar to “CrPV-like viruses” and have been described in the literature as either picornaviruses or picorna-like viruses. While many of these viruses remain relatively uncharacterized, for some e.g., Infectious flacherie virus (IFV) [AB000906] and Acyrthosiphon pisum virus (APV) [AF14514], the complete genome has been sequenced. These two viruses have been shown to have structural and organizational paradigms which are different again from the “CrPV-like viruses” genus. Amongst the remaining 20 or so viruses there are undoubtedly a number of viruses that will eventually be members of this genus but they are currently classified as unassigned viruses.
No proper name has been found for this genus.
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