IS481EU Shows a New Connection between Eukaryotic and Prokaryotic DNA Transposons.

DDD/E transposase gene is the most abundant gene in nature and many DNA transposons in all three domains of life use it for their transposition. A substantial number of eukaryotic DNA transposons show similarity to prokaryotic insertion sequences (ISs). The presence of IS 481 -like DNA transposons was indicated in the genome of Trichomonas vaginalis . Here, we surveyed IS 481 -like eukaryotic sequences using a bioinformatics approach and report a group of eukaryotic IS 481 -like DNA transposons, designated IS481EU , from parabasalids including T. vaginalis . The lengths of target site duplications (TSDs) of IS481EU are around 4 bps, around 15 bps, or around 25 bps, and strikingly, these discrete lengths of TSDs can be observed even in a single IS481EU family. Phylogenetic analysis indicated the close relationships of IS481EU with some of the prokaryotic IS 481 family members. IS481EU was not well separated from IS3EU / GingerRoot in the phylogenetic analysis, but was distinct from other eukaryotic DNA transposons including Ginger1 and Ginger2 . The unique characteristics of IS481EU in protein sequences and the distribution of TSD lengths support its placement as a new superfamily of eukaryotic DNA transposons.