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Mononegavirales



Mononegavirales
Virus classification
Group: Group V ((-)ssRNA)
Order: Mononegavirales
Families

Paramyxoviridae
Rhabdoviridae
Filoviridae
Bornaviridae

The Mononegavirales are an order of viruses comprising species that have a non-segmented, negative sense RNA genome. The order includes four families:

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.

Additional recommended knowledge

Contents

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.

Taxonomic Structure

Mononegavirales Families, Genera, and Species
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

Life cycle

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.

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.

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.

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.

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.

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).


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

 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Mononegavirales". A list of authors is available in Wikipedia.
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