Virus realms

Riboviria is a realm of viruses that includes all viruses that use a homologous RNA-dependent polymerase for replication. It includes RNA viruses that encode an RNA-dependent RNA polymerase, as well as reverse-transcribing viruses (with either RNA or DNA genomes) that encode an RNA-dependent DNA polymerase. RNA-dependent RNA polymerase (RdRp), also called RNA replicase, produces RNA (ribonucleic acid) from RNA. RNA-dependent DNA polymerase (RdDp), also called reverse transcriptase (RT), produces DNA (deoxyribonucleic acid) from RNA. These enzymes are essential for replicating the viral genome

Floreoviria is a realm of eukaryotic viruses that contains all viruses that encode a replication protein that has an N-terminal HUH superfamily endonuclease domain and a C-terminal superfamily 3 helicase domain, as well as all viruses descended from such viruses. Floreovirians typically have circular single-stranded DNA (ssDNA) genomes, but some have linear ssDNA genomes or circular double-stranded DNA (dsDNA) genomes. The prototypical members of the realm are commonly called CRESS-DNA viruses, which stands for circular, Rep-encoding ssDNA viruses. The replication (Rep) protein is involved in

taxonomic rank for viruses

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 r

Varidnaviria is a realm of viruses that includes all DNA viruses that encode major capsid proteins that contain two vertical jelly roll folds. The major capsid proteins (MCP) form into pseudohexameric subunits of the viral capsid, which stores the viral deoxyribonucleic acid (DNA). The jelly roll folds are vertical, or perpendicular, to the surface of the capsid. Apart from the double jelly roll fold MCP (DJR-MCP), most viruses in the realm share many other characteristics, such as minor capsid proteins (mCP) that has one vertical jelly roll fold, an ATPase that packages viral DNA into the cap

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.

Ribozyviria is a realm of satellite nucleic acids — infectious agents that resemble viruses, but cannot replicate without a helper virus. Established in ICTV TaxoProp 2020.012D, the realm is named after the presence of genomic and antigenomic ribozymes of the Deltavirus type. The agents in Ribozyviria are satellite nucleic acids, which are distinct from satellite viruses in that they do not encode all of their own structural proteins but require proteins from their helper viruses in order to assemble. Additional common features include a rod-like structure, an RNA-binding "delta antigen" encod