Revision 25799 of "Retrovirus" on enwiki

{{Taxobox_begin | color = violet | name = Retroviruses}}
{{Taxobox_begin_placement_virus}}
{{Taxobox_group_vi_entry}}
{{Taxobox_familia_entry | taxon = '''''Retroviridae'''''}}
{{Taxobox_end_placement}}
{{Taxobox_section_subdivision | color = violet | plural_taxon = Genera}}
''[[Alpharetrovirus]]''<br>
''[[Betaretrovirus]]''<br>
''[[Gammaretrovirus]]''<br>
''[[Deltaretrovirus]]''<br>
''[[Epsilonretrovirus]]''<br>
''[[Lentivirus]]''<br>
''[[Spumavirus]]''
{{Taxobox_end}}
A '''retrovirus''' is a [[virus]] which has a [[genome]] consisting of two identical plus sense [[RNA]] molecules. It relies on [[reverse transcriptase]] to perform a kind of reverse [[Transcription_(genetics)|transcription]] of its genome from [[RNA]] into [[DNA]] for insertion by [[integrase]] into the host's genome. The virus itself is just a storage form for its nucleic acid genome; the reverse transcription takes place in the host's [[cytosol]]. Any virus' genome integrated into the host's genome is called a [[provirus]].

While transcription usually works from DNA to RNA, reverse transcriptase transcribes RNA into DNA. The term "retro" in retrovirus refers to this reversal of the [[Crick's_central_dogma|central dogma]] of [[genetics]].

Because reverse transcription is missing the usual "proofreading" of DNA transcription, this kind of virus [[mutate|mutates]] very often. This enables the virus to grow [[resistance|resistant]] to antiviral pharmaceuticals quickly. That is one of the main reasons why an effective [[vaccine]] for [[HIV]] has not been developed yet.

Among others, retrovirus genomes commonly contain three [[gene]]s, that encode proteins that can be found back in the mature virus:
* ''gag'' codes for core and structural [[protein]]s of the virus.
* ''pol'' codes for reverse transcriptase, [[protease]] and [[integrase]].
* ''env'' codes for the virus coat proteins.

Four identified [[human]] retroviruses ([[HTLV]] 1&2, [[HIV]] 1&2) attack [[Helper T cell|CD4 cell]]s.
Another feature common to all retroviruses is a [[lipid]] envelope surrounding their [[capsid]]. It is essential for their function. This explains why retroviruses can be killed by just washing hands.

Studies of these viruses are what first demonstrated the synthesis of [[DNA]] from [[RNA]] templates, a fundamental mode for transferring genetic material that occurs in both [[eukaryote]]s and [[prokaryote]]s. Certain groups speculate that the processes followed by retroviruses (that is, RNA>DNA>RNA>Protein) may be the key to the [[evolution]] of DNA; thus, that in the "[[primordial soup]]," retroviruses evolved to create [[DNA]] from the [[RNA]] templates, and it was subsequently adopted by cellular organisms due to its increased stability.

The following genera are included here:
*Genus ''[[Alpharetrovirus]]''; type species: ''[[Avian leucosis virus]]''
*Genus ''[[Betaretrovirus]]''; type species: ''[[Mouse mammary tumour virus]]''
*Genus ''[[Gammaretrovirus]]''; type species: ''[[Murine leukeamia virus]]''; others include ''[[Feline leukemia virus]]''
*Genus ''[[Deltaretrovirus]]''; type species: ''[[Bovine leukaemia virus]]''; others include ''[[Human T-lymphotropic virus]]''
*Genus ''[[Epsilonretrovirus]]''; type species: ''[[Walleye dermal sarcoma virus]]''
*Genus ''[[Lentivirus]]''; type species: ''[[HIV|Human immunodeficiency virus 1]]''; others include ''[[Simian immunodeficiency virus|Simian]]'', ''[[Feline immunodeficiency virus|Feline]]'' immunodeficiency viruses
*Genus ''[[Spumavirus]]''; type species: ''[[Chimpanzee foamy virus]]''
These were previously divided into three subfamilies (''Oncovirinae'', ''Lentivirinae'', and ''Spumavirinae''), but with our current knowledge of retroviruses, this is no longer appropriate.

Note: Reverse transcriptase activity outside of retroviruses has been found in almost all eukaryotes, enabling the generation and insertion of new copies of retroposons into the genome.

==See also==
*[[sarcoma]] and [[leukaemia]]
*[[HIV]]

==External links==
* [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/R/Retroviruses.html Retroviruses]
* [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?call=bv.View..ShowTOC&rid=rv.TOC NCBI retrovirus book online]
[[Category:Molecular biology]][[Category:Viruses]][[Category:Retroviruses]]
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