Structure and evolution of the hAT transposon superfamily

The maize transposon Activator (Ac) was the first mobile DNA element to be discovered. Since then, other elements were found that share similarity to Ac, suggesting that it belongs to a transposon superfamily named hAT after hobo from Drosophila, Ac from maize, and Tam3 from snapdragon. We addressed the structure and evolution of hAT elements by developing new toot for tra nsposon mining and searching the public sequence databases for the hallmark s of hAT elements, namely the transposase and short terminal inverted repea ts (TIRs) flanked by 8-bp host duplications. We found 147 MT-related sequen ces in plants, animals, and fungi. Six conserved blocks could be identified in the transposase of most hAT elements. A total of 41 hAT sequences were flanked by TIRs and 8-bp host duplications and, out of these, 34 sequences had TIRs similar to the consensus determined in this work, suggesting that they are active or recently active transposons. Phylogenetic analysis and c lustering of hAT sequences suggest that the hAT superfamily is very ancient , probably predating the plant-fungi-animal separation, and that, unlike pr eviously proposed, there is no evidence that horizontal gene transfer was i nvolved in the evolution of hAT elements.