Duplodnaviria

Duplodnaviria
Illustrated comparison of Duplodnaviria virions
Virus classification
(unranked):	Virus
Realm:	Duplodnaviria
Kingdom:	Heunggongvirae
Subtaxa
See text
Synonyms[1][2]
HK97-like group HK97 major capsid protein supermodule

Duplodnaviria is a realm of viruses that includes all double-stranded DNA viruses that encode the HK97 fold major capsid protein. The HK97 fold major capsid protein (HK97 MCP) is the primary component of the viral capsid, which stores the viral deoxyribonucleic acid (DNA). Viruses in the realm also share a number of other characteristics, such as an icosahedral capsid, an opening in the capsid called a portal, a protease enzyme that empties the inside of the capsid prior to DNA packaging, and a terminase enzyme that packages viral DNA into the capsid. There are three groups of viruses in the realm: caudoviruses, herpesviruses, and the putative group mirusviruses.

Caudoviruses are one of the most abundant group of viruses on Earth and are ubiquitous worldwide. They infect prokaryotes and are a major cause of death in them, which contributes to the recycling of organic material in a process called viral shunt. Caudoviruses have been used as model organisms to study biological processes and as a form of therapy to treat bacterial infections. Herpesviruses infect animals and are commonly associated with diseases such as herpes and chickenpox. Mirusviruses infect microscopic eukaryotes and are among the most common eukaryotic viruses in sunlit oceans. Many duplodnavirians are able to enter a latent state in which they persist in cells without forming virions. This is called the lysogenic cycle and contrasts with the lytic cycle, which produces virions.

Duplodnaviria likely predates the last universal common ancestor (LUCA) of cellular life and was present in the LUCA. Caudoviruses in particular were likely already diverse by the time the LUCA emerged. Mirusviruses are related to viruses in the phylum Nucleocytoviricota in the realm Varidnaviria because they encode the core replication- and transcription-related proteins found in nucleocytoviruses. It is unclear, however, which realm these genes originate from. In any case, herpesviruses appear to have lost most of these genes through reductive evolution. Outside of the realm, an HK97-like fold is only found in encapsulins, which form nanocompartments in prokaryotes and are likely derived from duplodnaviruses.