Editing DNA virus (section)

===''Varidnaviria''===
[[File:2w0c_monomer.png|thumb|A [[ribbon diagram]] of the MCP of ''[[Pseudoalteromonas virus PM2]]'', with the two jelly roll folds colored in red and blue]]
''[[Varidnaviria]]'' contains DNA viruses that encode MCPs that have a [[jelly roll fold]] folded structure in which the jelly roll (JR) fold is perpendicular to the surface of the viral capsid. Many members also share a variety of other characteristics, including a minor capsid protein that has a single JR fold, an ATPase that packages the genome during capsid assembly, and a common [[DNA polymerase]]. Two kingdoms are recognized: ''[[Helvetiavirae]]'', whose members have MCPs with a single vertical JR fold, and ''[[Bamfordvirae]]'', whose members have MCPs with two vertical JR folds.<ref name=vari />

Varidnaviria is either monophyletic or polyphyletic and may predate the LUCA. The kingdom ''Bamfordvirae'' is likely derived from the other kingdom ''Helvetiavirae'' via [[Fusion gene|fusion]] of two MCPs to have an MCP with two jelly roll folds instead of one. The single jelly roll (SJR) fold MCPs of ''Helvetiavirae'' show a relation to a group of proteins that contain SJR folds, including the [[Cupin superfamily]] and [[nucleoplasmin]]s.<ref name=vari /><ref name=krupovic /><ref name=luca />

Marine viruses in ''Varidnaviria'' are ubiquitous worldwide and, like tailed bacteriophages, play an important role in marine ecology.<ref>{{cite journal|vauthors=Kauffman KM, Hussain FA, Yang J, Arevalo P, Brown JM, Chang WK, VanInsberghe D, Elsherbini J, Sharma RS, Cutler MB, Kelly L, Polz MF|date=1 February 2018|title=A Major Lineage of Non-Tailed dsDNA Viruses as Unrecognized Killers of Marine Bacteria|journal=Nature|volume=554|issue=7690|pages=118–122|doi=10.1038/nature25474|pmid=29364876|bibcode=2018Natur.554..118K|s2cid=4462007}}</ref> Most identified eukaryotic DNA viruses belong to the realm.<ref name=krupovic2015 >{{cite journal|vauthors=Krupovic M, Koonin EV|date=February 2015|title=Polintons: a hotbed of eukaryotic virus, transposon and plasmid evolution|journal=Nat Rev Microbiol|volume=13|issue=2|pages=105–115|doi=10.1038/nrmicro3389|pmc=5898198|pmid=25534808}}</ref> Notable disease-causing viruses in ''Varidnaviria'' include [[adenovirus]]es, [[poxvirus]]es, and the [[African swine fever virus]].<ref name=ictv >{{cite web|url=https://ictv.global/taxonomy|title=Virus Taxonomy: 2019 Release|website=International Committee on Taxonomy of Viruses|access-date=24 September 2020}}</ref> Poxviruses have been highly prominent in the history of modern medicine, especially ''Variola virus'', which caused [[smallpox]].<ref>{{cite journal|vauthors=Meyer H, Ehmann R, Smith GL|date=February 2020|title=Smallpox in the Post-Eradication Era|journal=Viruses|volume=12|issue=2|pages=138|doi=10.3390/v12020138|pmc=7077202|pmid=31991671|doi-access=free}}</ref> Many varidnaviruses can become endogenized in their host's genome; a peculiar example are [[virophage]]s, which after infecting a host, can protect the host against [[giant virus]]es.<ref name=krupovic2015 />