Ribozyviria

Ribozyviria is a realm of satellite nucleic acids — infectious agents that resemble viruses, but cannot replicate without a helper virus.[1] 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.[2] Additional common features include a rod-like structure, an RNA-binding "delta antigen" encoded in the genome, and animal hosts.[3] Furthermore, the size range of the genomes of these viruses is between around 1547–1735nt, they encode a hammerhead ribozyme or a hepatitis delta virus ribozyme, and their coding capacity only involves one conserved protein. Most lineages of this realm are poorly understood, the notable exception being the genus Deltavirus, comprising the causal agents of hepatitis D in humans.[4]

Kolmioviridae
Diagram of a Deltavirus virion
Virus classification Edit this classification
(unranked): Virus
Realm: Ribozyviria
Family: Kolmioviridae
Subtaxa
1 family
8 genera
15 species

See text

The realm Ribozyviria has an unclear evolutionary origin. It has been proposed that they may have derived from retrozymes (a family of retrotransposons) or a viroid-like element (i.e. viroids and satellites) with capsid protein capture.[4][5]

Taxonomy

Historical development

The first taxa of this realm to receive acceptance by the ICTV is the species Hepatitis delta virus and its genus Deltavirus, in 1993. Deltavirus remained unassigned to any higher taxa until 2018, when the ICTV mistakenly classified Deltavirus within the then newly established realm, Riboviria. In 2019, this error was rectified and Deltavirus returned to its original position. In 2020, Hepatitis delta virus was abolished and replaced with eight new species, and the taxonomy developed to reach its current form, detailed below.[6]

Current status

Ribozyviria contains a single family, Kolmioviridae, with no intermediate taxa between realm and family. This family contains eight genera.

The names of all genera in this realm allude to the letter D in various languages. The family name comes from Finnish kolmio "triangle," another reference to the Greek letter "Δ" (delta).[3]

This taxonomy is shown hereafter:[1]

See also

References
  1. "Virus Taxonomy: 2020 Release". International Committee on Taxonomy of Viruses (ICTV). March 2021. Retrieved 10 May 2021.
  2. Baez, John. "Subcellular Life Forms". University of California, Riverside. Retrieved 2020-06-04.
  3. Hepojoki J, Hetzel U, Paraskevopoulou S, Drosten C, Harrach B, Zerbini M, Koonin EV, Krupovic M, Dolja V, Kuhn JH (6 December 2020). "Create one new realm (Ribozyviria) including one new family (Kolmioviridae) including genus Deltavirus and seven new genera for a total of 15 species" (docx). International Committee on Taxonomy of Viruses (ICTV). Retrieved 27 May 2021.
  4. Lee, Benjamin D.; Koonin, Eugene V. (2022-01-12). "Viroids and Viroid-like Circular RNAs: Do They Descend from Primordial Replicators?". Life. 12 (1): 103. doi:10.3390/life12010103. ISSN 2075-1729. PMC 8781251. PMID 35054497.
  5. Netter, Hans J.; Barrios, Marilou H.; Littlejohn, Margaret; Yuen, Lilly K. W. (2021). "Hepatitis Delta Virus (HDV) and Delta-Like Agents: Insights Into Their Origin". Frontiers in Microbiology. 12: 1448. doi:10.3389/fmicb.2021.652962. ISSN 1664-302X. PMC 8256844. PMID 34234753.
  6. "Taxonomy History – Taxonomy – ICTV". talk.ictvonline.org. Retrieved 2021-10-08.
  7. Chang WS, Pettersson JH, Le Lay C, Shi M, Lo N, Wille M, Eden JS, Holmes EC (July 2019). "Novel hepatitis D-like agents in vertebrates and invertebrates". Virus Evolution. 5 (2): vez021. doi:10.1093/ve/vez021. PMC 6628682. PMID 31321078.
  8. Hetzel U, Szirovicza L, Smura T, Prähauser B, Vapalahti O, Kipar A, Hepojoki J (April 2019). "Identification of a Novel Deltavirus in Boa Constrictors". mBio. 10 (2). doi:10.1128/mBio.00014-19. PMC 6445931. PMID 30940697.
  9. Wille M, Netter HJ, Littlejohn M, Yuen L, Shi M, Eden JS, Klaassen M, Holmes EC, Hurt AC (December 2018). "A Divergent Hepatitis D-Like Agent in Birds". Viruses. 10 (12): 720. doi:10.3390/v10120720. PMC 6315422. PMID 30562970.
  10. Paraskevopoulou S, Pirzer F, Goldmann N, Schmid J, Corman VM, Gottula LT, Schroeder S, Rasche A, Muth D, Drexler JF, Heni AC, Eibner GJ, Page RA, Jones TC, Müller MA, Sommer S, Glebe D, Drosten C (July 2020). "Mammalian deltavirus without hepadnavirus coinfection in the neotropical rodent Proechimys semispinosus". Proceedings of the National Academy of Sciences of the United States of America. 117 (30): 17977–17983. doi:10.1073/pnas.2006750117. PMC 7395443. PMID 32651267.

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