Nucleocytoplasmic large DNA viruses

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Virus classification
Group: Group I (dsDNA)

Megaviridae (Mimiviridae and OLPG group)

The nucleocytoplasmic large DNA viruses, are a new order of viruses that contain the Megavirales or giant viruses.[1][2] There are nine families of nucleocytoplasmic large DNA viruses (NCLDV) that all share certain genomic and structural characteristics; however, it is uncertain whether the similarities of the different families of this group have a common viral ancestor.[3] One feature of this group is a large genome and the presence of many genes involved in DNA repair, DNA replication, transcription, and translation. Typically, viruses with smaller genomes do not contain genes for these processes. Most of the viruses in this family also replicate in both the host's nucleus and cytoplasm, thus the name nucleocytoplasmic.

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


Members of the family Ascoviridae come in different shapes. Some can be rod-shaped, while others are oval. They measure up to 130 nm wide and 400 nm long. Theses viruses have circular double stranded DNA that have a length of about 100–200 kilobase pairs. They infect lepidopteran insect larvae and can infect through parasitoid wasps. Once they infect they replicate and cause death in insect pest. This allows them to control insect populations.[4] Ascoviridae can have up to 180 genes in its genome. The replication of this virus takes place in the nucleus of the host cell. When it replicates, it causes the nucleus to increase in size and eventually burst. After, the virion starts to form and spread.[5]


A member of the family Asfarviridae is a known as an asfarvirus. This virus is the cause of African swine fever. Some of the symptoms for this flu include fever, high pulse, fast breathing, and it can cause death. These symptoms can be similar to those from hog cholera, the difference is that the African swine flu can not be cured. There is no vaccine developed to fight this virus.[6]


The Iridoviridae have linear double stranded DNA genomes up to 220 kilobases long and can code for about 211 proteins. The capsid of this virion is icosahedral shaped and can be up to 350 nm wide. The replication cycle of this virus begins in the nucleus of the host and end in the cytoplasm. Some families of this virus are often found infecting amphibians while other are found in insect and crustaceans.[7]


These viruses have double stranded DNA genomes that are about 372 kilobases long. Members of the family can have about 457 ORFs in its genome. The host organisms are amoeba. Once it infects, viral replication takes place in the cytoplasm.[citation needed] It was found that the genome of the family Marseilleviridae codes for about 28 different proteins.[8] The capsid of the marseillevirus is about 250 nm wide with a geometry shape of an icosahedral. The replication of this virus usually occurs near the nucleus once it infects the amoeba. Once the virus infects it can cause a shape change in the host’s nucleus.[9]


This family contains some of the largest viruses ever discovered. They have linear double stranded DNA genomes with the length of 1,259,197 base pairs, which is larger than some small bacteria. Within in this genome 1,100 proteins are coded. 74.76% of the base pairs are represented by thymine and adenine. The Megaviridae virus can be found infecting acanthamoeba or other protozoan clades.  Once the virus infects the host, the replication cycle takes place in the cytoplasm. Within the genome, DNA repair enzymes can be found. These are used when the DNA is harmed such as when it is exposed to ionizing radiation or UV light.[10]


Pandoraviridae Discovered in 2013 from a coastal water sample in Chile. It is mostly found infecting amoebae. It has a length of 1 micrometer long and .5 micrometer wide. Its genome can be up to 2.5 million base pairs long.[11] The replication of this virus take place in the cytoplasm. Like other giant viruses, it affect the host’s nucleus and can take up to 15 hours to start infecting.[12] Although it is found in water, it does not affect humans, it may actually help us by increasing the production of oxygen in aquatic environments.[13] 


The Phycodnaviridae are icosahedral in shape with a double-stranded DNA molecule. Some members of this family can have a linear double stranded DNA while others have a circular double stranded DNA. The genome has been found to be up to 560 kilobases in length. Up to 50% of the DNA can be represented by guanine or cytosine. This virus is known to infect algae, which means it is found in the ocean.[14]


The Pithoviridae have only two representatives. These viruses infects amoebas and can survive in low temperatures. For years this virus was believed to be frozen, but due to climate change it has begun to show up again.[15] This is a double stranded DNA virus with its size being 610 kilobases log. The genome is estimated to code for 476 open reading frames. The viron is rod shaped with a length of 1,100 nm long and 500 nm in diameter.[16]


The Poxviridae have a linear double-stranded DNA molecule that can have a length of up to 230 kilobases. The replication of these viruses takes place in the cytoplasm. Smallpox, cowpox, and other pox viruses belong to this family.[17] 

See also[edit]


  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 (5): 321–332. doi:10.1159/000336562. PMID 22508375.
  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 (12): 2517–21. doi:10.1007/s00705-013-1768-6. PMC 4066373. PMID 23812617.
  3. ^ Iyer, L. M.; Aravind, L.; Koonin, E. V. (December 2001). "Common Origin of Four Diverse Families of Large Eukaryotic DNA Viruses". Journal of Virology. 75 (23): 11720–34. doi:10.1128/JVI.75.23.11720-11734.2001. PMC 114758. PMID 11689653.
  4. ^ "Ascoviridae—Ascoviridae—dsDNA Viruses—International Committee on Taxonomy of Viruses (ICTV)". International Committee on Taxonomy of Viruses (ICTV). Retrieved 2017-12-07.
  5. ^ Asgari, Sassan; Bideshi, Dennis K; Bigot, Yves; Federici, Brian A; Cheng, Xiao-Wen (2017). "ICTV Virus Taxonomy Profile: Ascoviridae". The Journal of General Virology. 98 (1): 4–5. doi:10.1099/jgv.0.000677. ISSN 0022-1317. PMC 5370392. PMID 28218573.
  6. ^ "African swine fever (ASF) | animal disease". Encyclopedia Britannica. Retrieved 2017-12-07.
  7. ^ "Iridoviridae—Iridoviridae—dsDNA Viruses—International Committee on Taxonomy of Viruses (ICTV)". International Committee on Taxonomy of Viruses (ICTV). Retrieved 2017-12-07.
  8. ^ Boyer, Mickaël; Yutin, Natalya; Pagnier, Isabelle; Barrassi, Lina; Fournous, Ghislain; Espinosa, Leon; Robert, Catherine; Azza, Saïd; Sun, Siyang (2009-12-22). "Giant Marseillevirus highlights the role of amoebae as a melting pot in emergence of chimeric microorganisms". Proceedings of the National Academy of Sciences of the United States of America. 106 (51): 21848–21853. doi:10.1073/pnas.0911354106. ISSN 0027-8424. PMC 2799887. PMID 20007369.
  9. ^ Aherfi, Sarah (2014-10-01). "The expanding family Marseilleviridae". Virology. 466–467: 27–37. doi:10.1016/j.virol.2014.07.014. ISSN 0042-6822. PMID 25104553.
  10. ^ Arslan, Defne; Legendre, Matthieu; Seltzer, Virginie; Abergel, Chantal; Claverie, Jean-Michel (2011-10-18). "Distant Mimivirus relative with a larger genome highlights the fundamental features of Megaviridae". Proceedings of the National Academy of Sciences. 108 (42): 17486–17491. doi:10.1073/pnas.1110889108. ISSN 0027-8424. PMC 3198346. PMID 21987820.
  11. ^ Yong, Ed (2013). "Giant viruses open Pandora's box". Nature. doi:10.1038/nature.2013.13410.
  12. ^ Aherfi, Sarah; Colson, Philippe; La Scola, Bernard; Raoult, Didier (2016-03-22). "Giant Viruses of Amoebas: An Update". Frontiers in Microbiology. 7: 349. doi:10.3389/fmicb.2016.00349. ISSN 1664-302X. PMC 4801854. PMID 27047465.
  13. ^ "Biggest Virus Yet Found, May Be Fourth Domain of Life?". 2013-07-19. Retrieved 2017-12-07.
  14. ^ Wilson, W. H.; Van Etten, J. L.; Allen, M. J. (2009). "The Phycodnaviridae: The Story of How Tiny Giants Rule the World". Current Topics in Microbiology and Immunology. Current Topics in Microbiology and Immunology. 328: 1–42. doi:10.1007/978-3-540-68618-7_1. ISBN 978-3-540-68617-0. ISSN 0070-217X. PMC 2908299. PMID 19216434.
  15. ^ Ornes, Stephen (2017-07-31). "Return of the giant zombie virus". Science News for Students. Retrieved 2017-12-07.
  16. ^ "Pithovirus". Retrieved 2017-12-07.
  17. ^ Moss, Bernard (2013). "Poxvirus DNA Replication". Cold Spring Harbor Perspectives in Biology. 5 (9): a010199. doi:10.1101/cshperspect.a010199. ISSN 1943-0264. PMC 3753712. PMID 23838441.