Adnaviria

Adnaviria is a realm of archaeal viruses that have filamentous virions (i.e., bodies) and linear, double-stranded DNA genomes. Their genomes exist in A-form (A-DNA) and encode a dimeric major capsid protein (MCP) that contains the SIRV2 fold, an alpha-helix bundle with four helices. Adnavirians infect hyperthermophilic (very high temperature), thermoacidophilic (high temperature, highly acidic), and methanotrophic (methane-metabolizing) archaea. They can be found worldwide, though some are concentrated in extreme geothermal environments.

The extracellular particles (virions) of adnavirians consist of the genome encased in capsid proteins to form a helical nucleoprotein complex. For some of them, 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 stiff like a rod. In general, enveloped adnavirians are more flexible than non-enveloped ones. At both ends of the virion are protrusions involved in host recognition.