Editing Retrovirus (section)

==Classification==
[[Image:Phylogeny of Retroviruses.svg|thumb|upright=1.5|Phylogeny of Retroviridae]]

===Exogenous===
{{cleanup section|reason=Not the "Retroviridae" taxon the article talks about; suggest move into [[Baltimore classification#Reverse transcribing viruses]] or [[Revtraviricetes]].|date=February 2021}}

Exogenous retroviruses are infectious RNA- or DNA-containing viruses that are transmitted from one organism to another. In the [[Baltimore classification]] system, which groups viruses together based on their manner of [[messenger RNA]] synthesis, they are classified into two groups: Group VI: single-stranded RNA viruses with a DNA intermediate in their life cycle, and Group VII: double-stranded DNA viruses with an RNA intermediate in their life cycle.{{citation needed|date=May 2021}}

====Group VI viruses====
All members of [[Virus classification#Baltimore classification|Group VI]] use virally encoded [[reverse transcriptase]], an RNA-dependent DNA polymerase, to produce DNA from the initial virion RNA genome. This DNA is often integrated into the host genome, as in the case of retroviruses and [[Pseudoviridae|pseudoviruses]], where it is replicated and [[Transcription (genetics)|transcribed]] by the host.

Group VI includes:
* Order [[Ortervirales]]
** Family ''[[Belpaoviridae]]''
** Family ''[[Metaviridae]]''
** Family ''[[Pseudoviridae]]''
** Family ''[[Retroviridae]]'' – Retroviruses, e.g. [[HIV]]
** Family ''[[Caulimoviridae]]'' – a VII group virus family (see below)

The family ''Retroviridae'' was previously divided into three subfamilies (''Oncovirinae'', ''Lentivirinae'', and ''Spumavirinae''), but are now divided into two: ''Orthoretrovirinae'' and ''Spumaretrovirinae''. The term [[oncovirus]] is now commonly used to describe a cancer-causing virus. This family now includes the following genera:
* Subfamily ''[[Orthoretrovirinae]]'':
** Genus ''[[Alpharetrovirus]]''; including [[Avian leukosis virus]] and [[Rous sarcoma virus]]
** Genus ''[[Betaretrovirus]]''; including [[Mouse mammary tumour virus]]
** Genus ''[[Gammaretrovirus]]''; including [[Murine leukemia virus]] and [[Feline leukemia virus]]
** Genus ''[[Deltaretrovirus]]''; including [[Bovine leukemia virus]] and the cancer-causing'[[Human T-lymphotropic virus]]
** Genus ''[[Epsilonretrovirus]]''
** Genus ''[[Lentivirus]]''; including [[HIV|Human immunodeficiency virus 1]] and [[Simian immunodeficiency virus|Simian]] and [[Feline immunodeficiency virus|Feline]] immunodeficiency viruses
* Subfamily ''[[Spumaretrovirinae]]'':
** Genus ''[[Bovispumavirus]]''
** Genus ''[[Equispumavirus]]''
** Genus ''[[Felispumavirus]]''
** Genus ''[[Prosimiispumavirus]]''
** Genus ''[[Simian foamy virus|Simiispumavirus]]''

====Group VII viruses====
{{main|dsDNA-RT virus}}
Both families in [[Virus classification#Baltimore classification|Group VII]] have DNA genomes contained within the invading virus particles. The DNA genome is transcribed into both mRNA, for use as a transcript in protein synthesis, and pre-genomic RNA, for use as the template during genome replication. Virally encoded [[reverse transcriptase]] uses the pre-genomic RNA as a template for the creation of genomic DNA.

Group VII includes:
* Family ''[[Caulimoviridae]]'' — e.g. [[Cauliflower mosaic virus]]
* Family ''[[Hepadnaviridae]]'' — e.g. [[Hepatitis B virus]]
The latter family is closely related to the newly proposed
* Family ''[[Nackednaviridae]]'' — e.g. [[African cichlid nackednavirus]] (ACNDV), formerly named African cichlid hepatitis B virus (ACHBV).<ref name="Lauber2017">{{cite journal | vauthors = Lauber C, Seitz S, Mattei S, Suh A, Beck J, Herstein J, Börold J, Salzburger W, Kaderali L, Briggs JA, Bartenschlager R | display-authors = 6 | title = Deciphering the Origin and Evolution of Hepatitis B Viruses by Means of a Family of Non-enveloped Fish Viruses | journal = Cell Host & Microbe | volume = 22 | issue = 3 | pages = 387–399.e6 | date = September 2017 | pmid = 28867387 | pmc = 5604429 | doi = 10.1016/j.chom.2017.07.019 }} and [https://www.cell.com/cms/attachment/2119344051/2092493318/mmc1.pdf PDF]</ref>
whilst families ''[[Belpaoviridae]]'', ''[[Metaviridae]]'', ''[[Pseudoviridae]]'', ''[[Retroviridae]]'', and ''[[Caulimoviridae]]'' constitute the order ''[[Ortervirales]]''.<ref>{{cite journal | vauthors = Krupovic M, Blomberg J, Coffin JM, Dasgupta I, Fan H, Geering AD, Gifford R, Harrach B, Hull R, Johnson W, Kreuze JF, Lindemann D, Llorens C, Lockhart B, Mayer J, Muller E, Olszewski NE, Pappu HR, Pooggin MM, Richert-Pöggeler KR, Sabanadzovic S, Sanfaçon H, Schoelz JE, Seal S, Stavolone L, Stoye JP, Teycheney PY, Tristem M, Koonin EV, Kuhn JH | display-authors = 6 | title = Ortervirales: New Virus Order Unifying Five Families of Reverse-Transcribing Viruses | journal = Journal of Virology | volume = 92 | issue = 12 | date = June 2018 | pmid = 29618642 | pmc = 5974489 | doi = 10.1128/JVI.00515-18 }}</ref>

===Endogenous===
{{Main|Endogenous retrovirus}}
Endogenous retroviruses are not formally included in this classification system, and are broadly classified into three classes, on the basis of relatedness to exogenous genera:
* Class I are most similar to the gammaretroviruses
* Class II are most similar to the betaretroviruses and alpharetroviruses
* Class III are most similar to the spumaviruses.<ref>[https://www.nytimes.com/2020/05/09/technology/plandemic-judy-mikovitz-coronavirus-disinformation.html Virus Conspiracists Elevate a New Champion], by [[Davey Alba]], May 9, 2020, nytimes.com</ref>