Polintons (also called
Mavericks) are large
DNA which contain
with homology to
virus and which are often found in
eukaryotic . 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.
Properties
A typical polinton is around 15–20
in size, though examples have been described up to 40kb.
Polintons encode up to 10 proteins, the key elements being the protein-primed type B DNA polymerase and the
retroviral-like
integrase from which they derive their name. Polintons are sometimes referred to as "self-synthesizing" transposons, because they encode the proteins necessary to replicate themselves.
Most polintons also encode an
adenoviral-like cysteine protease, an
FtsK-like
ATPase, and proteins with homology to the
jelly-roll fold structure of
viral capsid proteins. The presence of putative capsid proteins has prompted suggestions that polintons may be able to form
under some conditions; however, this has not been demonstrated experimentally.
Polinton sequences contain terminal inverted repeats characteristic of transposable elements, usually on the order of 100–1000 base pairs.
Distribution
Polintons have been detected in all groups of eukaryotes other than the
Archaeplastida (containing
red algae,
green algae,
, and
). They are particularly common in
, a group that includes animals.
The
parasite Trichomonas vaginalis, which causes
trichomoniasis, has a unique genome composed of up to 30% polintons.
Evolution
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.
analyses of known polinton sequences support this ancestry model and suggest that transmission of polintons is mainly vertical
(though horizontal gene transfer of a polinton has been reported
).
The evolutionary relationships between polintons, double-stranded DNA viruses, and selfish genetic elements are complex. The first descriptions of polintons linked them by sequence relationship to , , and .
The Polisuviricotina subphylum 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.
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
which in 2005 were reported in transposable elements given the name
Mavericks by Cedric Feschotte and Ellen Pritham.
An overlapping class of transposable element was described in 2006 under the name
polintons, derived from the key proteins
polymerase and
integrase, by Vladimir Kapitonov and
Jerzy Jurka.
Both terms continue in common use.
Because of their viral capsid-like proteins and self-replication abilities, it has been suggested that polintons are capable of forming and would properly be termed polintoviruses.
