Nucleocytoplasmic large DNA viruses

Megavirales
Virus classification
Group: Group I (dsDNA)
Families

Ascoviridae
Asfarviridae
Iridoviridae
Marseilleviridae
Megaviridae
Mimiviridae
Pandoraviridae
Phycodnaviridae
Pithoviridae
Poxviridae

The nucleocytoplasmic large DNA viruses or NCLDV, proposed as a new order Megavirales (i.e., the giant viruses),[1][2] are a number of families of large DNA viruses:

  1. Ascoviridae
  2. Asfarviridae
  3. Iridoviridae
  4. Marseilleviridae
  5. Megaviridae
  6. Mimiviridae
  7. Pandoraviridae
  8. Phycodnaviridae
  9. Pithoviridae
  10. Poxviridae

Two unassigned genera, Dinodnavirus and Faustovirus, also belong to this clade. Another virus – Pacmanvirus – has been described.[3] This virus appears to be related to Faustovirus, Kaumoebavirus and the Asfarviridae. Also Mollivirus and Ectocarpus siliculosus virus (ESV-1) have been placed into this clade.[4] Another virus that appears to be distantly related to the Pithoviridae family is Cedratvirus lausannensis.[5]

Reasons for NCLDV grouping

All have both common and unique features of genomic DNA and virion structure. It remains uncertain whether the similarities of different families of this group have a common viral ancestor, although the latter theory is controversial and under heavy scrutiny.[6]

There are 47 NCLDV core genes currently recognised. These include the four key proteins involved in DNA replication and repair. These include the enzymes DNA polymerase family B, the topoisomerase II A, the FLAP endonuclease and the processing factor proliferating cell nuclear antigen. Other proteins include the DNA dependent RNA polymerase II and transcription factor II B.

It is probable that these viruses evolved before the separation of eukaryotes into the extant crown groups. The ancestral genome was complex with at least 41 genes, including: (1) the replication machinery; (2) up to four RNA polymerase subunits; (3) at least three transcription factors; (4) capping and polyadenylation enzymes; (5) the DNA packaging apparatus; (6) structural components of an icosahedral capsid and the viral membrane.

See also

References

  1. ↑ Colson P, de Lamballerie X, Fournous G, Raoult D (2012). "Reclassification of giant viruses composing a fourth domain of life in the new order Megavirales". Intervirology. 55: 321–332. PMID 22508375. doi:10.1159/000336562.
  2. ↑ Colson P, De Lamballerie X, Yutin N, Asgari S, Bigot Y, Bideshi DK, Cheng XW, Federici BA, Van Etten JL, Koonin EV, La Scola B, Raoult D (2013). ""Megavirales", a proposed new order for eukaryotic nucleocytoplasmic large DNA viruses". Arch Virol. 158: 2517–21. PMC 4066373 Freely accessible. PMID 23812617. doi:10.1007/s00705-013-1768-6.
  3. ↑ Andreani J, Bou Khalil JY, Sevvana M, Benamar S, Di Pinto F, Bitam I, Colson P, Klose T, Rossmann M, Raoult D, La Scola B (2017) Pacmanvirus, a new giant icosahedral virus at the crossroads between Asfarviridae and Faustoviruses. J Virol pii: JVI.00212-17. doi: 10.1128/JVI.00212-17
  4. ↑ F. Maumus, G. Blanc: Study of Gene Trafficking between Acanthamoeba and Giant Viruses Suggests an Undiscovered Family of Amoeba-Infecting Viruses. Genome Biol Evol (2016) 8 (11): 3351-3363, 09.11.2016. doi: 10.1093/gbe/evw260
  5. ↑ Bertelli C, Mueller L, Thomas V, Pillonel T, Jacquier N, Greub G (2017) Cedratvirus lausannensis - digging into Pithoviridae diversity. Environ Microbiol doi: 10.1111/1462-2920.13813
  6. ↑ Iyer, L. M.; Aravind, L.; Koonin, E. V. (December 2001). "Common Origin of Four Diverse Families of Large Eukaryotic DNA Viruses". 75 (23): 11720–34. PMC 114758 Freely accessible. PMID 11689653. doi:10.1128/y.


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