RNA virus 26195 221644581 2008-06-25T12:54:22Z 202.141.146.194 /* Group IV - positive-sense ssRNA viruses */ An '''RNA virus''' is a [[virus]] that has [[RNA]] (ribonucleic acid) as its [[genetic material]].<ref>[http://www.nlm.nih.gov/cgi/mesh/2008/MB_cgi?mode=&term=RNA+Viruses&field=entry MeSH], retrieved on 12 April 2008.</ref> This [[nucleic acid]] is usually single-stranded RNA (ssRNA) but may be double-stranded RNA (dsRNA).<ref name=Pattonrnav>{{cite book | author = Patton JT (editor). | title = Segmented Double-stranded RNA Viruses: Structure and Molecular Biology | publisher = Caister Academic Press | year = 2008 | url=http://www.horizonpress.com/rnav | id = [http://www.horizonpress.com/rnav ISBN 978-1-904455-21-9]}}</ref> The [[International Committee on Taxonomy of Viruses|ICTV]] classifies RNA viruses as those that belong to ''Group III'', ''Group IV'' or ''Group V'' of the [[Virus classification#Baltimore classification|Baltimore classification]] system of classifying viruses, and does not consider viruses with DNA intermediates as RNA viruses.<ref name="titleListing in Taxonomic Order - Index to ICTV Species Lists">{{cite web |url=http://www.ncbi.nlm.nih.gov/ICTVdb/Ictv/fr-fst-g.htm |title=Listing in Taxonomic Order - Index to ICTV Species Lists |accessdate=2008-04-11 |format= |work=}}</ref> Notable human diseases caused by RNA viruses include [[SARS]], [[influenza]] and [[hepatitis C]]. ==Characteristics== ===Single-stranded RNA viruses and RNA Sense=== RNA viruses can be further classified according to the sense or polarity of their RNA into [[Sense (molecular biology)|negative-sense]] and [[Sense (molecular biology)|positive-sense]], or ambisense RNA viruses. Positive-sense viral RNA is identical to viral mRNA and thus can be immediately [[translation (genetics)|translated]] by the host cell. Negative-sense viral RNA is complementary to mRNA and thus must be converted to positive-sense RNA by an [[RNA polymerase]] before translation. As such, purified RNA of a positive-sense virus can directly cause infection though it may be less infectious than the whole virus particle. Purified RNA of a negative-sense virus is not infectious by itself as it needs to be [[Transcription (genetics)|transcribed]] into positive-sense RNA. [[Ambisense]] RNA viruses resemble negative-sense RNA viruses, except they also translate genes from the positive strand.<ref>{{cite journal |author=Nguyen M, Haenni AL |title=Expression strategies of ambisense viruses |journal=Virus Res. |volume=93 |issue=2 |pages=141–50 |year=2003 |pmid=12782362 | doi = 10.1016/S0168-1702(03)00094-7 <!--Retrieved from CrossRef by DOI bot-->}}</ref> ===Double-stranded RNA viruses=== {{further|[[Double-stranded RNA viruses]]}} The [[Double-stranded RNA viruses|double-stranded (ds)RNA viruses]] represent a diverse group of viruses that vary widely in host range (humans, animals, plants, [[fungi]], and [[bacteria]]), [[genome]] segment number (one to twelve), and [[virion]] organization (T-number, [[capsid]] layers, or turrets). Members of this group include the [[rotavirus]]es, renowned globally as the commonest cause of [[gastroenteritis]] in young children, and [[bluetongue virus]] <ref name=sobrino7>{{cite book |chapterurl=http://www.horizonpress.com/avir|author=Roy P|year=2008|chapter=Molecular Dissection of Bluetongue Virus|title=Animal Viruses: Molecular Biology|publisher=Caister Academic Press|id=[http://www.horizonpress.com/avir ISBN 978-1-904455-22-6]}}</ref> <ref name=roy2>{{cite book |chapterurl=http://www.horizonpress.com/rnav|author=Roy P|year=2008|chapter=Structure and Function of Bluetongue Virus and its Proteins|title=Segmented Double-stranded RNA Viruses: Structure and Molecular Biology|publisher=Caister Academic Press|id=[http://www.horizonpress.com/rnav ISBN 978-1-904455-21-9]}}</ref>, an economically important pathogen of cattle and sheep. In recent years, remarkable progress has been made in determining, at atomic and subnanometeric levels, the structures of a number of key viral proteins and of the virion capsids of several dsRNA viruses, highlighting the significant parallels in the structure and replicative processes of many of these viruses. <ref name=Pattonrnav>{{cite book | author = Patton JT (editor). | title = Segmented Double-stranded RNA Viruses: Structure and Molecular Biology | publisher = Caister Academic Press | year = 2008 | url=http://www.horizonpress.com/rnav | id = [http://www.horizonpress.com/rnav ISBN 978-1-904455-21-9]}}</ref> ===Mutation rates=== RNA viruses generally have very high [[mutation]] rates as they lack [[DNA polymerase]]s which can find and fix mistakes, and are therefore unable to conduct [[DNA repair]] of damaged genetic material. [[DNA virus]]es have considerably lower mutation rates due to the proof-reading ability of DNA polymerases within the host cell. [[Retrovirus]]es have a high mutation rate even though their DNA intermediate integrates into the host genome (and is thus subject to host DNA proofreading once integrated), because errors during reverse transcription are embedded into both strands of DNA prior to integration. Although RNA usually mutates rapidly, recent work found that the SARS virus and related RNA viruses contain a gene that mutates very slowly.<ref name=Robertson_2005>{{cite journal | author=Robertson MP, Igel H, Baertsch R, Haussler D, Ares M Jr, Scott WG | title=The structure of a rigorously conserved RNA element within the SARS virus genome | journal=PLoS Biol | year=2005 | pages = e5 | volume=3 | issue=1 | pmid=15630477 {{DOI|10.1371/journal.pbio.0030005}} | doi = 10.1371/journal.pbio.0030005 <!--Retrieved from CrossRef by DOI bot-->}}</ref> The gene in question has a complex three-dimensional structure which is hypothesized to provide a chemical function necessary for viral propagation, perhaps as a [[ribozyme]]. If so, most mutations would render it unfit for that purpose and would not propagate. ==Replication== Animal RNA viruses are [http://www.ncbi.nlm.nih.gov/ICTVdb/Ictv/fr-fst-g.htm classified] into three distinct groups depending on their genome and mode of replication (and the numerical groups based on the older [[Virus_classification#Baltimore_classification|Baltimore classification]]): *[[Double-stranded RNA viruses]] (Group III) contain from one to a dozen different RNA molecules, each of which codes for one or more viral proteins. *[[RNA_virus#Group_IV_-_positive-sense_ssRNA_viruses|Positive-sense ssRNA viruses]] (Group IV) have their genome directly utilized as if it were mRNA, producing a single protein which is modified by host and viral proteins to form the various proteins needed for replication. One of these includes [[RNA-dependent RNA polymerase]], which copies the viral RNA to form a double-stranded replicative form, in turn this directs the formation of new virions. *[[RNA_virus#Group_V_-_negative-sense_ssRNA_viruses|Negative-sense ssRNA viruses]] (Group V) must have their genome copied by an [[RNA polymerase]] to form positive-sense RNA. This means that the virus must bring along with it the [[RNA-dependent RNA polymerase]] enzyme. The positive-sense RNA molecule then acts as viral mRNA, which is translated into proteins by the host [[ribosomes]]. The resultant protein goes on to direct the synthesis of new virions, such as [[capsid]] proteins and RNA replicase, which is used to produce new negative-sense RNA molecules. [[Retrovirus]]es (Group VI) have a single-stranded RNA genome but are usually not considered RNA viruses because they use DNA intermediates to replicate. [[Reverse transcriptase]], a viral enzyme that comes from the virus itself after it is uncoated, converts the viral RNA into a complementary strand of DNA, which is copied to produce a double stranded molecule of viral DNA. After this DNA is [[integrase|integrated]], expression of the encoded genes may lead the formation of new virions. ==Group III - dsRNA viruses== *Family ''[[Birnaviridae]]'' *Family ''[[Chrysoviridae]]'' *Family ''[[Cystoviridae]]'' *Family ''[[Hypoviridae]]'' *Family ''[[Partitiviridae]]'' *Family ''[[Reoviridae]]'' - includes [[Rotavirus]] *Family ''[[Totiviridae]]'' *Unassigned genera ** ''[[Endornavirus]]'' ==Group IV - positive-sense ssRNA viruses== *Order ''[[Nidovirales]]'' **Family ''[[Arterivirus|Arteriviridae]]'' **Family ''[[Coronaviridae]]'' - includes [[Coronavirus]], [[Severe Acute Respiratory Syndrome|SARS]] **Family ''[[Okavirus|Roniviridae]]'' *Unassigned **Family ''[[Astroviridae]]'' **Family ''[[Barnavirus|Barnaviridae]]'' **Family ''[[Bromoviridae]]'' **Family ''[[Caliciviridae]]'' - includes [[Norwalk virus]] **Family ''[[Closteroviridae]]'' **Family ''[[Comoviridae]]'' **Family ''[[Dicistroviridae]]'' **Family ''[[Flaviviridae]]'' - includes [[Yellow fever]] virus, [[West Nile virus]], [[Hepatitis C virus]], [[Dengue fever]] virus **Family ''[[Flexiviridae]]'' **Family ''[[Leviviridae]]'' **Family ''[[Luteoviridae]]'' - includes [[Barley yellow dwarf virus]] **Family ''[[Marnavirus|Marnaviridae]]'' **Family ''[[Narnaviridae]]'' **Family ''[[Nodaviridae]]'' **Family ''[[Picornaviridae]]'' - includes [[Poliovirus]], the [[Rhinovirus|common cold]] virus, [[Hepatitis A]] virus **Family ''[[Potyviridae]]'' **Family ''[[Sequiviridae]]'' **Family ''[[Tetraviridae]]'' **Family ''[[Togaviridae]]'' - includes [[Rubella]] virus, [[Ross River virus]], [[Sindbis virus]],[[Chikungunya virus]] **Family ''[[Tombusviridae]]'' **Family ''[[Tymoviridae]]'' **Unassigned genera ***Genus ''[[Benyvirus]]'' ***Genus ''[[Cheravirus]]'' ***Genus ''[[Furovirus]]'' ***Genus ''[[Hepevirus]]'' - includes [[Hepatitis E]] virus ***Genus ''[[Hordeivirus]]'' ***Genus ''[[Idaeovirus]]'' ***Genus ''[[Ourmiavirus]]'' ***Genus ''[[Pecluvirus]]'' ***Genus ''[[Pomovirus]]'' ***Genus ''[[Sadwavirus]]'' ***Genus ''[[Sobemovirus]]'' ***Genus ''[[Tobamovirus]]'' - includes [[tobacco mosaic virus]] ***Genus ''[[Tobravirus]]'' ***Genus ''[[Umbravirus]]'' ==Group V - negative-sense ssRNA viruses== *Order ''[[Mononegavirales]]'' **Family ''[[Borna disease|Bornaviridae]]'' - [[Borna disease virus]] **Family ''[[Filoviridae]]'' - includes [[Ebola]] virus, [[Marburg virus]] **Family ''[[Paramyxoviridae]]'' - includes [[Measles]] virus, [[Mumps virus]], [[Nipah virus]], [[Hendra virus]] **Family ''[[Rhabdoviridae]]'' - includes [[Rabies]] virus *Unassigned **Family ''[[Arenaviridae]]'' - includes [[Lassa virus]] **Family ''[[Bunyaviridae]]'' - includes [[Hantavirus]] **Family ''[[Orthomyxoviridae]]'' - includes [[Influenza]] viruses **Unassigned genera: ***Genus ''[[Deltavirus]]'' ***Genus ''[[Ophiovirus]]'' ***Genus ''[[Tenuivirus]]'' ***Genus ''[[Varicosavirus]]'' ==See also== *[[Virus classification]] *[[Virus#Replication|Viral replication]] *[[Sense (molecular biology)|Positive/negative-sense]] *[[Animal virology|Animal viruses]] *[[Double-stranded RNA viruses]] *[[Retrovirus]] *[[DNA viruses]] {{Viruses}} ==References== {{reflist}} *Prescott, L. (1993). Microbiology, Wm. C. Brown Publishers, ISBN 0-697-01372-3 ==External links== * {{MeshName|RNA+Viruses|3=RNA Viruses}} *[http://www.horizonpress.com/gateway/animal-viruses.html Animal viruses] [[Category:Virology]] [[Category:RNA]] [[Category:Microbiology]] [[bg:РНК вирус]] [[de:RNA-Virus]] [[es:Virus ARN]] [[eo:(-)ve ĉensenca ssRNA Viruso]] [[fr:Virus à ARN]] [[hu:RNS-vírus]] [[nl:RNA-virus]] [[ja:RNAウイルス]] [[pl:Wirusy RNA]] [[pt:Vírus ARN]] [[zh:核糖核酸病毒]]