eukaryotic genomes. 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, a DNA polymerase and a retroviral-like integrase.[1][2][3][4][5]
Properties
A typical polinton is around 15–20
virions under some conditions; however, this has not been demonstrated experimentally.[3][5][7]
Polinton sequences contain
terminal inverted repeats characteristic 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
Polintons have been detected in all groups of eukaryotes other than the
The genetic network linking various types of Bamfordvirae viruses and selfish genetic elements, represented by labeled circles. Links between circles are color-coded by the gene whose sequence homology establishes the link.[8]
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.
Phylogenetic analyses of known polinton sequences support this ancestry model and suggest that transmission of polintons is mainly vertical[6] (though horizontal gene transfer of a polinton has been reported[9]
Maveriviricetes class of viruses is named after their resemblance to Maverick/Polinton transposons. All the viruses mentioned are united under Bamfordvirae for 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
Giant transposable elements were originally discovered in the mid-2000s, beginning with the description of a novel family of
retroviral-like integrase proteins[11] which were then associated with transposable elements given the name Mavericks.[2][12] Meanwhile, an overlapping class of transposable element was described under the name polintons, derived from the key proteins polymerase and integrase, by Vladimir Kapitonov and Jerzy 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 forming
virions and would properly be termed polintoviruses.[7] However, this terminology is not yet accepted and awaits experimental validation of the virion hypothesis.[3][4]
