Polinton
Polintons(also calledMavericks) are largeDNAtransposonswhich containgeneswithhomologytoviralproteinsand which are often found ineukaryoticgenomes.They were first discovered in the mid-2000s and are the largest and most complex known DNA transposons. Polintons encode up to 10 individual proteins and derive their name from two key proteins, aDNApolymeraseand a retroviral-likeintegrase.[1][2][3][4][5]
Properties
[edit]A typical polinton is around 15–20kilobase pairsin size, though examples have been described up to 40kb.[6]Polintons encode up to 10 proteins, the key elements being theprotein-primed type B DNA polymeraseand theretroviral-likeintegrasefrom which they derive their name. Polintons are sometimes referred to as "self-synthesizing" transposons, because they encode the proteins necessary to replicate themselves.[5]Most polintons also encode anadenoviral-likecysteine protease,anFtsK-likeATPase,and proteins withhomologyto thejelly-roll foldstructure ofviral capsidproteins. The presence of putative capsid proteins has prompted suggestions that polintons may be able to formvirionsunder some conditions; however, this has not been demonstrated experimentally.[3][5][7]
Polinton sequences containterminal inverted repeatscharacteristic of transposable elements, usually on the order of 100–1000 base pairs.[3]They also possess a 6bp target site duplication sequence at the insertion site.[6]
Distribution
[edit]Polintons have been detected in all groups of eukaryotes other than theArchaeplastida(containingred algae,green algae,glaucophytes,andland plants). They are particularly common inunikonts,a group that includes animals.[3]ThepathogenicparasiteTrichomonas vaginalis,which causestrichomoniasis,has a unique genome composed of up to 30% polintons.[2]
Evolution
[edit]
Early descriptions of polintons identified them as likely to be ancient, at least one billion years old and possibly associated with an early ancestor of modern eukaryotes.[1]Phylogeneticanalyses of known polinton sequences support this ancestry model and suggest that transmission of polintons is mainly vertical[6](thoughhorizontal gene transferof a polinton has been reported[9]).
The evolutionary relationships between polintons,double-stranded DNA viruses,andselfish genetic elementsare complex. The first descriptions of polintons linked them by sequence relationship tolinear plasmids,bacteriophages,andadenoviruses.[1]More recently, relationships have been identified between polintons,virophages,andgiant viruses.Polintons are increasingly thought to form one component of a complex genetic network linking selfish genetic elements in eukaryotic genomes with double-stranded DNA viruses. Through homology in at least one and usually several genes, polintons are evolutionarily linked tolinear plasmids,virophages(especiallyMavirus virophage,familyLavidaviridae),giant viruses(Megavirales),Ginger 1 transposons,Tlr1 transposons,transpovirons,eukaryotic viruses of theAdenoviridaefamily, andbacteriophagesof theTectiviridaefamily.[3][5][8]
TheMaveriviricetesclass of viruses is named after their resemblance to Maverick/Polinton transposons. All the viruses mentioned are united underBamfordviraefor their double jelly-roll capsid.[10]Some polinton-like viruses (PLVs) other than Tlr1 have also been identified, and are yet to be put into a taxon (presumably under Maveriviricetes).[3]
Discovery and nomenclature
[edit]Giant transposable elements were originally discovered in the mid-2000s, beginning with the description of a novel family ofretroviral-likeintegraseproteins[11]which in 2005 were reported in transposable elements given the nameMavericksby Cedric Feschotte and Ellen Pritham.[2][12]An overlapping class of transposable element was described in 2006 under the namepolintons,derived from the key proteinspolymerase andintegrase, byVladimir KapitonovandJerzy Jurka.[1]Both terms continue in common use.[3][6]
Because of their viral capsid-like proteins and self-replication abilities, it has been suggested that polintons are capable of formingvirionsand would properly be termedpolintoviruses.[7]However, this terminology is not yet accepted and awaits experimental validation of the virion hypothesis.[3][4]
References
[edit]- ^abcdKapitonov, V. V.; Jurka, J. (14 March 2006)."Self-synthesizing DNA transposons in eukaryotes".Proceedings of the National Academy of Sciences.103(12): 4540–4545.Bibcode:2006PNAS..103.4540K.doi:10.1073/pnas.0600833103.PMC1450207.PMID16537396.
- ^abcPritham, Ellen J.; Putliwala, Tasneem; Feschotte, Cédric (April 2007). "Mavericks, a novel class of giant transposable elements widespread in eukaryotes and related to DNA viruses".Gene.390(1–2): 3–17.doi:10.1016/j.gene.2006.08.008.PMID17034960.
- ^abcdefghKrupovic, Mart; Koonin, Eugene V. (22 December 2014)."Polintons: a hotbed of eukaryotic virus, transposon and plasmid evolution".Nature Reviews Microbiology.13(2): 105–115.doi:10.1038/nrmicro3389.PMC5898198.PMID25534808.
- ^abYutin, Natalya; Shevchenko, Sofiya; Kapitonov, Vladimir; Krupovic, Mart; Koonin, Eugene V. (11 November 2015)."A novel group of diverse Polinton-like viruses discovered by metagenome analysis".BMC Biology.13(1): 95.doi:10.1186/s12915-015-0207-4.PMC4642659.PMID26560305.
- ^abcdKrupovic, Mart; Koonin, Eugene V (June 2016)."Self-synthesizing transposons: unexpected key players in the evolution of viruses and defense systems".Current Opinion in Microbiology.31:25–33.doi:10.1016/j.mib.2016.01.006.PMC4899294.PMID26836982.
- ^abcdHaapa-Paananen, Saija; Wahlberg, Niklas; Savilahti, Harri (September 2014). "Phylogenetic analysis of Maverick/Polinton giant transposons across organisms".Molecular Phylogenetics and Evolution.78:271–274.doi:10.1016/j.ympev.2014.05.024.PMID24882428.
- ^abKrupovic, Mart; Bamford, Dennis H; Koonin, Eugene V (2014)."Conservation of major and minor jelly-roll capsid proteins in Polinton (Maverick) transposons suggests that they are bona fide viruses".Biology Direct.9(1): 6.doi:10.1186/1745-6150-9-6.PMC4028283.PMID24773695.
- ^abYutin, Natalya; Raoult, Didier; Koonin, Eugene V (2013)."Virophages, polintons, and transpovirons: a complex evolutionary network of diverse selfish genetic elements with different reproduction strategies".Virology Journal.10(1): 158.doi:10.1186/1743-422X-10-158.PMC3671162.PMID23701946.
- ^Dupuy, C.; Periquet, G.; Serbielle, C.; Bézier, A.; Louis, F.; Drezen, J-M (31 March 2011). "Transfer of a chromosomal Maverick to endogenous bracovirus in a parasitoid wasp".Genetica.139(4): 489–496.doi:10.1007/s10709-011-9569-x.PMID21451967.S2CID20901926.
- ^Koonin EV, Dolja VV, Krupovic M, Varsani A, Wolf YI, Yutin N, Zerbini M, Kuhn JH (October 2019)."Create a megataxonomic framework, filling all principal taxonomic ranks, for DNA viruses encoding vertical jelly roll-type major capsid proteins".ICTV Proposal (Taxoprop):2019.003G.doi:10.13140/RG.2.2.14886.47684.
- ^Gao, X; Voytas, D (March 2005). "A eukaryotic gene family related to retroelement integrases".Trends in Genetics.21(3): 133–137.doi:10.1016/j.tig.2005.01.006.PMID15734571.
- ^Feschotte, C; Pritham, E (October 2005). "Non-mammalian c-integrases are encoded by giant transposable elements".Trends in Genetics.21(10): 551–552.doi:10.1016/j.tig.2005.07.007.PMID16084623.