Drosophila X virus
| Drosophila X virus | |
|---|---|
| Virus classification | |
| Group: | Group III (dsRNA) |
| Order: | Unassigned |
| Family: | Birnaviridae |
| Genus: | Entomobirnavirus |
| Species: | Drosophila X virus |
Drosophila X virus (DXV) belongs to the Birnaviridae family of viruses. Birnaviridae currently consists of three genera. The first genus is Entomobirnavirus, which contains DXV. The next genus is Aquabirnavirus, containing infectious pancreatic necrosis virus (IPNV). The last genus is Avibirnavirus, which contains infectious bursal disease virus (IBDV). All of these genera contain homology in three specific areas of their transcripts. The homology comes from the amino and carboxyl regions of preVP2, a small 21-residue-long domain near the carboxyl terminal of VP3, and similar small ORFs sequences.
DXV was named after Drosophila melanogaster, where it was first isolated. DXV was first isolated and named in 1978. DXV was discovered as a contaminant in adult D. melanogaster while studying rhabdoviruses. Assay results of DXV showed that DXV induces sensitivity to both carbon dioxide and NH2, which suggests general anoxia. Therefore, the pathogenic pathway for DXV leads to anoxia sensitivity and death of D. melanogaster. By negative contrast electron microscopy the DXV components were first visualized. The origin of DXV is unknown and unclear. It was thought that DXV could have been pre-existent in Drosophila broods in a non-pathogenic form. Additionally, it was speculated that DXV might have originated as a contaminant from fetal calf serum in infection type studies because it was documented that endogenous bovine viruses were already in fetal calf serum.
DXV is a Baltimore Class III naked (non-enveloped) virus. The capsid of this protein contains an icosahedral geometry (T=13) consisting of 260 trimeric VP2 capsomeres. Specifically, DXV contains a bi-segmented dsRNA genome. Both segments of the DXV genome contain 5’ terminal GGA triplet and a 3’ terminal CCC triplet consensus, which is consistent with birnaviridae (Shwed, 2002). The segment A genome is 3360-bp in length. Segment A encodes a polyprotein sequence as follows: NH2-preVP2-VP4-VP3-COOH. This segment contains a large and small ORF. The segment B genome is 2991-bp in length. Segment B encodes a polypeptide sequence as follows: NH2-VP1-COOH. The 5’ UTR of segment B is homologous to segment A, but unlike segment A, there is only one ORF. Unusually, VP1 can be in two forms; as a free RdRp and as the genome-liked protein (VpG) that attaches to both 5’ end segments of the DXV through a Ser-5’-GMP phosphodiester bond. The replication of DXV follows the characterized dsRNA virus replication cycle.
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