| Adnaviria | |
|---|---|
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| |
| Acidianus filamentous virus 3 (AFV3) virion | |
Virus classification 
| |
| (unranked): | Virus |
| Realm: | Adnaviria |
| Kingdom: | Zilligvirae |
| Phylum: | Taleaviricota |
| Class: | Tokiviricetes |
| Subtaxa | |
Adnaviria is a realm of viruses that includes archaeal viruses that have a filamentous virion (i.e. body) and a linear, double-stranded DNA genome.[1] The genome exists in A-form (A-DNA) and encodes a dimeric major capsid protein (MCP) that contains the SIRV2 fold, a type of alpha-helix bundle containing four helices. The virion consists of the genome encased in capsid proteins to form a helical nucleoprotein complex. For some viruses, this helix is surrounded by a lipid membrane called an envelope. Some contain an additional protein layer between the nucleoprotein helix and the envelope. Complete virions are long and thin and may be flexible or a stiff like a rod.
Adnaviria was established in 2020 after cryogenic electron microscopy showed that the viruses in the realm were related due to a shared MCP, A-DNA, and general virion structure. Viruses in Adnaviria infect hyperthermophilic archaea, i.e. archaea that inhabit very high temperature environments such as hot springs. Their A-DNA genome may be an adaptation to this extreme environment. Viruses in Adnaviria have potentially existed for a long time, as it is thought that they may have infected the last archaeal common ancestor. In general, they show no genetic relation to any viruses outside the realm.