Mononegavirales
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| Mononegavirales | ||||
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| Virus classification | ||||
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| Families | ||||
The Mononegavirales are an order of viruses comprising species that have a non-segmented, negative sense RNA genome. The order includes four families:
- Bornaviridae (Borna disease virus)
- Rhabdoviridae (e.g. Rabies virus)
- Filoviridae (eg Marburg virus, Ebola virus)
- Paramyxoviridae (eg Newcastle disease virus, measles virus)
A number of important human diseases, both established (mumps, measles, rabies) and emerging (ebola haemorrhagic fever, borna disease, Hendra virus, Nipah virus), are caused by viruses from this order.
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[edit] Structure
Virions possess an envelope and a helical nucleocapsid containing an RNA-dependent RNA polymerase (RDRP) and genomic RNA. The genome contains 6-10 genes, although a process known as RNA editing allows for a greater number of gene products.
[edit] Taxonomic Structure
| Family | Subfamily | Genus | Species (* signifies type species) |
| Bornaviridae | Bornavirus | Borna disease virus * | |
| Filoviridae | Marburgvirus | Lake Victoria marburgvirus * | |
| Ebolavirus | Zaire virus * | ||
| Ivory Coast ebolavirus | |||
| Reston ebolavirus | |||
| Sudan ebolavirus | |||
| Paramyxoviridae | Paramyxovirinae | Respirovirus | Bovine parainfluenza virus 3 |
| Human parainfluenza virus 1 | |||
| Human parainfluenza virus 3 | |||
| Sendai virus * | |||
| Simian virus 10 | |||
| Morbillivirus | Canine distemper virus | ||
| Cetacean morbillivirus | |||
| Dolphin distemper virus | |||
| Measles virus * | |||
| Peste-des-petits-ruminants virus | |||
| Phocine distemper virus | |||
| Rinderpest virus | |||
| Rubulavirus | Human parainfluenza virus 2 | ||
| Human parainfluenza virus 4 | |||
| Human parainfluenza virus 4a | |||
| Mapuera virus | |||
| Mumps virus * | |||
| Porcine rubulavirus | |||
| Simian virus 5 | |||
| Simian virus 41 | |||
| Henipavirus | Hendra virus * | ||
| Nipah virus | |||
| Avulavirus | Avian paramyxovirus | ||
| Newcastle disease virus | |||
| Pneumovirinae | Pneumovirus | Human respiratory syncytial virus * | |
| Bovine respiratory syncytial virus | |||
| Murine pneumonia virus | |||
| Metapneumovirus | Avian metapneumovirus * | ||
| Human metapneumovirus | |||
| Viruses in the family Paramyxoviridae that are not assigned to a genus | Tupaia paramyxovirus | ||
| Fer-de-Lance virus | |||
| Menangle virus | |||
| Nariva virus | |||
| Tioman virus | |||
| Rhabdoviridae | Vesiculovirus | Carajas virus | |
| Chandipura virus | |||
| Cocal virus | |||
| Isfahan virus | |||
| Maraba virus | |||
| Piry virus | |||
| Vesicular stomatitis Alagoas virus | |||
| Vesicular stomatitis Indiana virus * | |||
| Vesicular stomatitis New Jersey virus | |||
| Lyssavirus | Australian bat lyssavirus | ||
| Duvenhage virus | |||
| European bat lyssavirus | |||
| Lagos bat virus | |||
| Mokola virus | |||
| Rabies virus * | |||
| Ephemerovirus | Adelaide River virus | ||
| Berrimah virus | |||
| Bovine ephemeral fever virus * | |||
| Novirhabdovirus | Hirame rhabdovirus | ||
| Infectious hematopoietic necrosis virus | |||
| Viral hemorrhagic septicemia virus | |||
| Snakehead rhabdovirus | |||
| Cytorhabdovirus | Barley yellow striate mosaic virus | ||
| Broccoli necrotic yellows virus | |||
| Festuca leaf streak virus | |||
| Lettuce necrotic yellows virus * | |||
| Northern cereal mosaic virus | |||
| Sonchus virus | |||
| Strawberry crinkle virus | |||
| Wheat American striate mosaic virus | |||
| Nucleorhabdovirus | Datura yellow vein virus | ||
| Eggplant mottled dwarf virus | |||
| Maize mosaic virus | |||
| Potato yellow dwarf virus * | |||
| Rice yellow stunt virus | |||
| Sonchus yellow net virus | |||
| Sowthistle yellow vein virus | |||
| There are numerous viruses in the Rhabdoviridae family that are not assigned to a genus | |||
[edit] Life cycle
[edit] Entry
Viral particles enter a cell by binding to a cell surface receptor (eg sialic acid) and inducing fusion between the viral envelope and the cell membrane. In the cytoplasm, the particle uncoats, releasing the genome.
[edit] mRNA synthesis
The genomic sequence is negative sense, therefore it does not code for proteins. Complementary sequences must first be transcribed by an RNA-dependent RNA polymerase (RDRP). This inability of the genome to produce proteins requires the virion to carry the RDRP with it into the cell. This is in contrast to positive strand viruses which can synthesise RDRP once inside the cell.
The RDRP released from the viral particle binds to the single promoter site at the 3' end of the genome and begins transcription. The RDRP pauses at the gap between each gene, releasing the completed mRNA. Transcription can then either terminate or continue transcribing the next gene. This creates a polarity of transcription, where genes close to the 3' end of the genome are transcribed in the greatest abundance, whilst those towards the 5' end are least likely to be transcribed, since the RDRP has more opportunities to terminate. By placing the genes in order of required abundance from most to least, the virus is able to use this polarity as a form of transcriptional regulation. As a consequence, most genomes begin with the gene for the nucleocapsid protein and end with the gene for the RDRP.
[edit] Protein synthesis and genome synthesis
Once mRNA production has begun, the cellular protein translation system is co-opted to produce viral proteins which accumulate in the cytoplasm. At some point, possibly determined by the concentration of nucleocapsid protein, the RDRP molecules transcribing the viral genome begin ignoring the gap sequences between genes and produce full-length, positive-strand antigenomes. These are in turn transcribed into negative strand viral genome copies.
[edit] Assembly and exit
The newly synthesised viral proteins and genomes self-assemble and accumulate near the inside of the cell membrane. The virions bud off from the cell, gaining an envelope from the cell membrane as they exit. The new viral particle infects another cell to repeat the cycle.
[edit] RNA editing
RNA editing is a mechanism used by some members of Mononegavirales to produce multiple proteins from a single gene. It occurs when the RDRP enzyme inserts extra residues into the mRNA being synthesised. This creates a frame-shift, altering the amino acid sequence encoded by the mRNA.
[edit] Evolution
As with other RNA viruses that do not have a DNA intermediate, members of Mononegavirales are able to evolve at a rapid rate due to the absence of proof-reading ability in the RDRP enzyme. A high mutation rate occurs in the production of new genomes (up to 1 per 1000 bases).
[edit] External links
[edit] References
Büchen-Osmond, C. (2003). 01. Mononegavirales. In: ICTVdB - The Universal Virus Database, version 3. Retrieved April 6, 2004 from http://www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB/index.htm
Dewhurst, S. (2003) University of Rochester Medical Center Department of Microbiology and Immunology Selected Virology Lecture Notes. Retrieved April 6, 2004 from http://www.urmc.rochester.edu/smd/mbi/grad2/pdf/gr03nns.pdf
