Giant virus
| Giant virus | |
|---|---|
| Virus classification | |
| Group: | Group I (dsDNA)
|
A Giant Virus, sometimes referred to as a girus (a contraction of giant virus or gigantic virus), refers to a very large virus.[1][2] They are giant nucleocytoplasmic large DNA viruses (NCLDVs), having unique genes not found in other life, with separate phylogenic trees for those genes.[3]
Description
While the exact criteria as defined in the scientific literature vary, giant viruses are generally described as viruses having large pseudo-icosahedral capsids (200 to 400 nanometers) surrounded by a thick (approximately 100 nm) layer of filamentous protein fibers with large double-stranded DNA genomes (300 to 1000 kilobase pairs or larger) encoding a large contingent of genes (of the order of 1000 genes).[3][4] While few have been characterized in detail, the most notable examples of giruses are the phylogenetically related megavirus and mimivirus, belonging to the Megaviridae and Mimiviridae families, respectively, having the largest capsid diameters of all known viruses.[3][4]
Viral replication in giant viruses occurs within large circular virus factories located within the cytoplasm of the infected host cell, similar to the replication mechanism used by Poxviridae, though whether this mechanism is employed by all giant viruses or only mimivirus and the related mamavirus has yet to be determined.[4] These virion replication factories are themselves subject to infection by the virophage satellite viruses, which inhibit or impair the reproductive capabilities of the complementary virus.
Genetics and evolution
The genomes of giant viruses are the largest known for viruses, and contain genes that encode for important elements of translation machinery, a characteristic that had previously been believed to be indicative of cellular organisms. These genes include multiple genes encoding a number of aminoacyl tRNA synthetases, enzymes that catalyze the esterification of specific amino acids or their precursors to their corresponding cognate tRNAs to form an aminoacyl tRNA, that is then used during translation.[4] The presence of four aminoacyl tRNA synthetase encoding genes in mimivirus and mamavirus genomes, both species within the Mimiviridae family, as well as the discovery of seven aminoacyl tRNA synthetase genes, including the four genes present in Mimiviridae, in the megavirus genome provide evidence for a possible scenario in which these large DNA viruses evolved from a shared ancestral cellular genome by means of genome reduction.[4]
The discovery and subsequent characterization of these giant viruses has triggered some debate concerning the evolutionary origins of the giruses, going so far as to suggest that the giruses provide evidence of a fourth domain of life.[4][5]
Comparison of largest known giant viruses
Table 1 : Largest giant viruses with complete sequenced genomes
| Giant virus name | Genome Length | Genes | Capsid diameter (nm) | Hair cover | Genbank # |
|---|---|---|---|---|---|
| Megavirus chilensis[6] | 1,259,197 | 1120 proteins (predicted) | 440 | yes (75 nm) | JN258408 |
| Mamavirus[7] | 1,191,693 | 1023 proteins (predicted) | 390 | yes (120 nm) | JF801956 |
| Mimivirus[8][9] | 1,181,549 | 979 proteins 39 non-coding | 390 | yes (120 nm) | NC_014649 |
The whole list is in the Giant Virus Toplist created by the Giant Virus Finder software.
Table 2: Specific common features among giant viruses
| Giant virus name | Aminoacyl-tRNA synthetase | Octocoral-like 1MutS | 2Stargate[10] | Known virophage[11] | Cytoplasmic virion factory | Host |
|---|---|---|---|---|---|---|
| Megavirus chilensis | 7 (Tyr, Arg, Met, Cys, Trp, Asn, Ile) | yes | yes | no | yes | Acanthamoeba (Unikonta, Amoebozoa) |
| Mamavirus | 4 (Tyr, Arg, Met, Cys) | yes | yes | yes | yes | Acanthamoeba (Unikonta, Amoebozoa) |
| Mimivirus | 4 (Tyr, Arg, Met, Cys) | yes | yes | yes | yes | Acanthamoeba (Unikonta, Amoebozoa) |
1Mutator S (MutS) and its homologs are a family of DNA mismatch repair proteins involved in the mismatch repair system that acts to correct point mutations or small insertion/deletion loops produced during DNA replication, increasing the fidelity of replication. 2A stargate is a five-pronged star structure present on the viral capsid forming the portal through which the internal core of the particle is delivered to the host's cytoplasm.
See also
References
- ^ Reynolds, Kelly A. (2010). "Mysterious Microbe in Water Challenges the Very Definition of a Virus" (PDF). Water Conditioning & Purification. Archived from the original (PDF) on 2014-03-19.
{{cite journal}}: Unknown parameter|deadurl=ignored (|url-status=suggested) (help) - ^ Ogata, Hiroyuki; Kensuke Toyoda; Yuji Tomaru; Natsuko Nakayama; Yoko Shirai; Jean-Michel Claverie; Keizo Nagasaki (2009). "Remarkable sequence similarity between the dinoflagellate-infecting marine girus and the terrestrial pathogen African swine fever virus". Virology Journal. 6 (178): 178. doi:10.1186/1743-422X-6-178. PMC 2777158. PMID 19860921. Retrieved 30 May 2011.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ^ a b c Van Etten, James L. (July–August 2011). "Giant Viruses". American Scientist. 99 (4): 304–311. doi:10.1511/2011.91.304.
- ^ a b c d e f Legendre, Matthieu; Defne Arslan; Chantal Abergel; Jean-Michel Claverie (2012). "Genomics of Megavirus and the elusive fourth domain of Life". Communicative & Integrative Biology. 5 (1): 102–6. doi:10.4161/cib.18624. PMC 3291303. PMID 22482024.
- ^ Fileé J, Chandler M. (2012) Unpacking the Baggage: Origin and Evolution of Giant Viruses. In: G.Witzany (ed). Viruses: Essential Agents of Life. Springer, 203–216. ISBN 978-94-007-4898-9.
- ^ Arslan, D.; Legendre, M.; Seltzer, V.; Abergel, C.; Claverie, J.-M. (2011). "Distant Mimivirus relative with a larger genome highlights the fundamental features of Megaviridae". Proceedings of the National Academy of Sciences. 108 (42): 17486–91. doi:10.1073/pnas.1110889108. PMC 3198346. PMID 21987820.
- ^ Colson, P.; Yutin, N.; Shabalina, S. A.; Robert, C.; Fournous, G.; La Scola, B.; Raoult, D.; Koonin, E. V. (2011). "Viruses with More Than 1,000 Genes: Mamavirus, a New Acanthamoeba polyphaga mimivirus Strain, and Reannotation of Mimivirus Genes". Genome Biology and Evolution. 3: 737–42. doi:10.1093/gbe/evr048. PMC 3163472. PMID 21705471.
- ^ Raoult, D.; Audic, S; Robert, C; Abergel, C; Renesto, P; Ogata, H; La Scola, B; Suzan, M; Claverie, JM (2004). "The 1.2-Megabase Genome Sequence of Mimivirus". Science. 306 (5700): 1344–50. doi:10.1126/science.1101485. PMID 15486256.
- ^ Legendre, Matthieu; Santini, Sébastien; Rico, Alain; Abergel, Chantal; Claverie, Jean-Michel (2011). "Breaking the 1000-gene barrier for Mimivirus using ultra-deep genome and transcriptome sequencing". Virology Journal. 8 (1): 99. doi:10.1186/1743-422X-8-99. PMC 3058096. PMID 21375749.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ^ Zauberman, Nathan; Mutsafi, Yael; Halevy, Daniel Ben; Shimoni, Eyal; Klein, Eugenia; Xiao, Chuan; Sun, Siyang; Minsky, Abraham (2008). Sugden, Bill (ed.). "Distinct DNA Exit and Packaging Portals in the Virus Acanthamoeba polyphaga mimivirus". PLoS Biology. 6 (5): e114. doi:10.1371/journal.pbio.0060114. PMC 2430901. PMID 18479185.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ^ Fischer, M. G.; Suttle, C. A. (2011). "A Virophage at the Origin of Large DNA Transposons". Science. 332 (6026): 231–4. doi:10.1126/science.1199412. PMID 21385722.