Varidnaviria

The name "Varidnaviria" is a portmanteau of various DNA viruses and the suffix -viria, which is the suffix used for virus realms. Double-stranded DNA (dsDNA) viruses in the realm are often called non-tailed or tailless dsDNA viruses to distinguish them from the tailed dsDNA viruses of Duplodnaviria. ==Characteristics==

MCP, mCP, and ATPase Most viruses in Varidnaviria contain a capsid that is made of major capsid proteins (MCPs) that contain vertical double jelly roll (DJR) folds. The major capsid proteins are named so because they are the primary proteins that the capsid is made of. A jelly roll fold is a type of folded structure in a protein in which eight antiparallel beta strands are organized into four antiparallel beta sheets in a layout resembling a jelly roll, also called a Swiss roll. Each beta strand is a specific sequence of amino acids, and these strands bond to their antiparallel strands via hydrogen bonds. A double jelly roll fold MCP is one that has two jelly roll folds in a single protein. Vertical folds are those that are perpendicular to the capsid surface, in contrast to horizontal folds that are parallel to the capsid surface. During the process of assembling the viral capsid, MCPs self-assemble into hexagonal structures, called hexons, that contain three copies of the MCP. Hexons then bond to form the relatively flat triangular sides of the capsid, which is icosahedral in shape with 20 triangular faces and 12 vertices. Most members of the realm also encode genome packaging ATPases of the FtsK-HerA superfamily. The ATPases in Varidnaviria are enzymes that package the viral DNA into the capsid during the process of assembling virions. The exact function of the ATPase for some viruses in Varidnaviria is unclear since morphological features, such as the circular, supercoiled genome of bacteriophage PM2, seemingly prohibit translocation by the ATPase of DNA from outside the capsid to the inside. as do adenoviruses, which instead encode their own ATPase that has the same role. Other characteristics Apart from the core morphogenetic triad of traits (the MCP, mCP, and ATPase), certain other characteristics are common or unique in various lineages within Varidnaviria, listed hereafter. • All members of Varidnaviria, except for the family Finnlakeviridae, have dsDNA genomes. Viruses in Finnlakeviridae instead have single-stranded DNA (ssDNA) genomes. • In some unrelated • Some varidnavirians have special vertices in their icosahedral capsids for transporting the genome out of the capsid and for making virus factories. ==Phylogenetics==

Varidnaviria may predate the last universal common ancestor (LUCA) of cellular life, and viruses in the realm may have been present in the LUCA. The DJR-MCP appears to share common ancestry with the GH172/DUF2961 family of proteins as they appear to be sister clades. DUF2961 proteins are widespread in both prokaryotes and eukaryotes and are mainly involved in carbohydrate metabolism and binding. They form trimers with a pseudohexagonal shape that resembles the capsomeres of viral DJR-MCPs. Other cellular proteins that appear to be distantly related to the DJR-MCP and DUF2961 proteins include peptide:N-glycosidase F (PNGase F) and peptidylglycine α-hydroxylating monooxygenase (PHM). The two jelly rolls shared by these proteins are likely the result of a gene duplication event of a cellular single jelly roll fold prior to the emergence of Varidnaviria, though it is possible that the DJR evolved independently via gene duplication in both the DUF2961 and Varidnaviria lineages. and various RNA viruses in Riboviria also encode MCPs that have jelly roll folds, but they are horizontal (parallel) to the capsid surface, in contrast to the jelly roll folds of Varidnaviria, which are vertical (perpendicular) to the capsid surface. ==Classification==

Varidnaviria has two kingdoms: Abadenavirae and Bamfordvirae. Abadenavirae is monotypic down to the rank of phylum. This taxonomy can be visualized as follows: • Kingdom: Abadenavirae, which contains all prokaryotic DJR-MCP viruses except tectiviruses (Tectiliviricetes) • Phylum: Produgelaviricota • Kingdom: Bamfordvirae, which contains tectiviruses (Tectiliviricetes) and all eukaryotic DJR-MCP viruses Nearly all varidnavirians belong to Group I: dsDNA viruses of the Baltimore classification system, which groups viruses together based on how they produce messenger RNA and is commonly used alongside virus taxonomy, which is based on evolutionary history. The exception is viruses of the family Finnlakeviridae in the kingdom Abadenavirae, which have ssDNA genomes and belong to Group II: ssDNA viruses in the Baltimore system. Realms are the highest level of taxonomy used for viruses and Varidnaviria is one of ten. The others are Adnaviria, Duplodnaviria, Efunaviria, Floreoviria, Pleomoviria, Riboviria, Ribozyviria, Singelaviria, and Volvereviria. ==Interactions with hosts==

Disease Disease-causing viruses in Varidnaviria include adenoviruses, poxviruses, and the African swine fever virus (ASFV). Adenoviruses typically cause mild respiratory, gastrointestinal, and conjunctival illnesses, but occasionally cause more severe illnesses, such as hemorrhagic cystitis, hepatitis, and meningoencephalitis. Poxviruses infect many animals and typically cause non-specific symptoms paired with a characteristic rash that is called a pox. Poxviruses include Variola virus, which causes smallpox, and Vaccinia virus, which is used as the vaccine against smallpox. ASFV is usually asymptomatic in its natural reservoirs but causes a lethal hemorrhagic fever in domestic pigs that is a concern for agricultural production. Endogenization Many viruses in Varidnaviria encode the enzyme integrase and integrate their genome into the genome of their host. Polintons, which constitute the class Polintoviricetes, Endogenization is common among bacterial and archaeal DJR-MCP viruses. Virophages replicate by hijacking the replication apparati of giant viruses, thereby suppressing the number of giant virus virions produced, which increases the likelihood of host survival. Some virophages are able to become endogenized, and this endogenization can be considered a form of adaptive immunity for the host against giant virus infection. Bacteriophages in Varidnaviria are similarly a potential major cause of death among marine prokaryotes due to their large numbers. Autolykiviruses, a group of marine bacterial viruses, have broad host ranges that enable them to infect and kill many different bacteria species. ==History==

Diseases caused by poxviruses have been known for much of recorded history. Smallpox in particular has been highly prominent in modern medicine. The first vaccine to be invented protected against smallpox, and smallpox would later become the first disease to be eradicated. With the increased knowledge of the viruses of the realm, Varidnaviria was established in 2019 based on the shared traits of viruses in the realm. and may be more numerous than tailed dsDNA viruses of Duplodnaviria, the largest and most diverse lineage of viruses documented. The discovery of cellular proteins that contain a DJR-fold, however, led to further research that showed that the DJR MCPs of Varidnaviria likely evolved from said cellular proteins independent from vertical SJR-MCP viruses. Because of this, the SJR-MCP-encoding viruses of Helvetiavirae were given their own realm, Singelaviria. ==See also==