Homologues of bacterial TnpB_ IS605 are widespread in diverse eukaryotic transposable elements

Background Bacterial insertion sequences (IS) of IS200 / IS605 and IS607 family often encode a transposase (TnpA) and a protein of unknown function, TnpB. Results Here 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). Conclusions The 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.