Abstract
BackgroundBacterial insertion sequences (IS) of IS200/IS605 and IS607 family often encode a transposase (TnpA) and a protein of unknown function, TnpB.ResultsHere we report two groups of TnpB-like proteins (Fanzor1 and Fanzor2) that are widespread in diverse eukaryotic transposable elements (TEs), and in large double-stranded DNA (dsDNA) viruses infecting eukaryotes. Fanzor and TnpB proteins share the same conserved amino acid motif in their C-terminal half regions: D-X(125, 275)-[TS]-[TS]-X-X-[C4 zinc finger]-X(5,50)-RD, but are highly variable in their N-terminal regions. Fanzor1 proteins are frequently captured by DNA transposons from different superfamilies including Helitron, Mariner, IS4-like, Sola and MuDr. In contrast, Fanzor2 proteins appear only in some IS607-type elements. We also analyze a new Helitron2 group from the Helitron superfamily, which contains elements with hairpin structures on both ends. Non-autonomous Helitron2 elements (CRe-1, 2, 3) in the genome of green alga Chlamydomonas reinhardtii are flanked by target site duplications (TSDs) of variable length (approximately 7 to 19 bp).ConclusionsThe phylogeny and distribution of the TnpB/Fanzor proteins indicate that they may be disseminated among eukaryotic species by viruses. We hypothesize that TnpB/Fanzor proteins may act as methyltransferases.
Highlights
Bacterial insertion sequences (IS) of IS200/IS605 and IS607 family often encode a transposase (TnpA) and a protein of unknown function, TnpB
Identification of the eukaryotic TnpB-like proteins During a systematic screening of Transposable elements (TEs), a prototype of the eukaryotic TnpB-IS200/IS605-like protein was first discovered in the genome of the fungus Spizellomyces punctatus
The immediate homologues of the SPu-1-1p were found in some related eukaryotes, but distant homologues were identified among TnpB proteins encoded by bacterial insertions elements (ISs) from the IS200/IS605 and IS607 families
Summary
Bacterial insertion sequences (IS) of IS200/IS605 and IS607 family often encode a transposase (TnpA) and a protein of unknown function, TnpB. Transposable elements (TEs) are DNA segments that are duplicated and inserted into genomic DNA by a variety of mechanisms. There are two major groups of TEs: DNA transposons and retrotransposons. Retrotranposons are further divided into those containing long terminal repeats (LTRs), or LTR retrotransposons, and non-LTR retrotransposons, which are not flanked by LTRs. Typically, TEs encode only proteins essential for their reproduction and insertion, including reverse transcriptases and transposases (Tpases). There are four known types of transposases encoded by TEs. The most common type is the DDE-transposase encoded by most bacterial insertion sequences (IS), eukaryotic DNA transposons, and LTR retrotransposons. The second group is represented by reverse transcriptases (RT), encoded by a variety of non-
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