Singelaviria

Singelaviria
Virus classification
(unranked):	Virus
Realm:	Singelaviria
Kingdom:	Helvetiavirae
Phylum:	Dividoviricota
Class:	Laserviricetes
Order:	Halopanivirales
Subtaxa
See text

Singelaviria is a realm of viruses that includes all DNA viruses that encode major capsid proteins that contain a single vertical jelly roll fold. All viruses in Singelaviria have two major capsid proteins (MCPs) that both have a single jelly roll (SJR) fold. The MCPs form into pseudohexameric subunits of the viral capsid, which stores the viral deoxyribonucleic acid (DNA), and are vertical, or perpendicular, to the surface of the capsid. Apart from the SJR fold MCP (SJR-MCP), viruses in the realm also share a minor capsid protein (mCP) that also has a vertical SJR, an ATPase that packages viral DNA into the capsid, capsids that are icosahedral in shape, and a lipid membrane inside the capsid that surrounds the viral genome.

Viruses in Singelaviria infect archaea that inhabit highly saline environments and bacteria that inhabit high-temperature environments. Their genomes consist of double-stranded DNA that is either linear or circular in shape. Some viruses in the realm are capable of replication both by the lytic cycle, which produces virions, and the lysogenic cycle, in which the virus resides in the host cell as an episome. Some viruses in the realm have spikes on the vertices of their capsid that are shaped like horns or propellers.

From 2019 to 2024, viruses in Singelaviria were classified in the realm Varidnaviria, which contains DNA viruses that encode MCPs that have two vertical jelly roll folds. It was originally believed that such viruses were descended from singelavirians, but further research showed that the two groups of viruses have separate evolutionary origins, so the SJR-MCP lineage was given its own realm, Singelaviria, in 2025. It is believed by virologists that the two MCPs of singelavirians are the result of a gene duplication event of a single MCP encoded by a portoglobovirus-like virus.