Riboviria

Riboviria
Clockwise from top left: TEM of avian coronavirus, polio virus, bacteriophage Qβ, Ebolavirus, tobacco mosaic virus, Influenza A virus, Rotavirus, HIV-1. Center: homologous RT and RdRps with conserved palm domain.
Virus classification
(unranked):	Virus
Realm:	Riboviria
Kingdoms
Orthornavirae Pararnavirae

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 and transcribing viral genes into messenger RNA (mRNA) for translation of viral proteins.

Riboviria was established in 2018 to accommodate all RdRp-encoding RNA viruses and was expanded a year later to also include RdDp-encoding viruses. These two groups of viruses are assigned to two separate kingdoms: Orthornavirae for RdRp-encoding RNA viruses, and Pararnavirae for RdDp-encoding viruses, i.e. all reverse-transcribing viruses. Most identified eukaryotic viruses belong to the realm, including most human, animal, and plant viruses. Historically, few prokaryotic RNA viruses had been discovered to be included in the realm, but in the 2020s metagenomic and metatranscriptomic studies have discovered many prokaryotic RNA viruses.

Many of the most widely known viral diseases are caused by viruses in Riboviria, which includes coronaviruses, ebola virus, HIV, influenza viruses, and the rabies virus. These viruses and others in the realm have been prominent throughout history, including Tobacco mosaic virus, which was the first virus to be discovered. Many reverse-transcribing viruses integrate their genome into the genome of their host as part of their replication cycle. As a result of that, it is estimated that about 7–8% of the human genome originates from these viruses.