Paramyxoviridae
| Paramyxoviridae | |
|---|---|
| Virus classification | |
| Group: | Group V ((−)ssRNA) |
| Order: | Mononegavirales |
| Family: | Paramyxoviridae |
| Genera | |
Paramyxoviridae (from Greek para-, beyond, -myxo-, mucus or slime, plus virus, from Latin poison, slime, thus meaning "slime beyond slime"; sometimes abbreviated PMV) is a family of viruses in the order Mononegavirales. Humans, vertebrates, and birds serve as natural hosts. There are currently 38 species in this family, divided among 7 genera. Diseases associated with this negative-sense single-stranded RNA virus family include measles, mumps, and respiratory tract infections.
Table legend: "*" denotes type species.
Beilong virus is now known to be a member of the family. It was isolated from rat kidney and its pathogenic potential is unknown. J virus is very similar to Beilong virus and probably belongs in the same genus. Both have features that differ from the other genera in this family. Tailam virus may also belong in this genus. The genus Jeilongvirus has been proposed for these three viruses.
The relations between the salmon paramyxoviruses and the others have been poorly studied to date and their relationship to the other members of this genus is not currently known.
Viral replication is cytoplasmic. Entry into the host cell is achieved by virus attachment to host cell. Replication follows the negative stranded RNA virus replication model. Negative stranded RNA virus transcription, using polymerase stuttering is the method of transcription. Translation takes place by leaky scanning, ribosomal shunting, and RNA termination-reinitiation. The virus exits the host cell by budding. Human, vertebrates, and birds serve as the natural host. Transmission route is air borne particles.
Virions are enveloped and can be spherical, filamentous or pleomorphic. The diameter is around 150 nm. Genomes are linear, around 15kb in length. Fusion proteins and attachment proteins appear as spikes on the virion surface. Matrix proteins inside the envelope stabilise virus structure. The nucleocapsid core is composed of the genomic RNA, nucleocapsid proteins, phosphoproteins and polymerase proteins.
The genome is non-segmented negative-sense RNA, 15–19 kilobases in length and contains 6–10 genes. Extracistronic (non-coding) regions include:
Each gene contains transcription start/stop signals at the beginning and end, which are transcribed as part of the gene.
Gene sequence within the genome is conserved across the family due to a phenomenon known as transcriptional polarity (see Mononegavirales) in which genes closest to the 3’ end of the genome are transcribed in greater abundance than those towards the 5’ end. This is a result of structure of the genome. After each gene is transcribed, the RNA-Dependent RNA polymerase pauses to release the new mRNA when it encounters an intergenic sequence. When the RNA polymerase is paused, there is a chance that it will dissociate from the RNA genome. If it dissociates, it must reenter the genome at the leader sequence, rather than continuing to transcribe the length of the genome. The result is that the further downstream genes are from the leader sequence, the less they will be transcribed by RNA polymerase.
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