DNA synthesis is considered a defining feature in the movement of transposable 
elements. In determining the mechanism of piggyBac transposition, an insect 
transposon that is being increasingly used for genome manipulation in a variety 
of systems including mammalian cells, we have found that DNA synthesis can be 
avoided during piggyBac transposition, both at the donor site following 
transposon excision and at the insertion site following transposon integration. 
We demonstrate that piggyBac transposon excision occurs through the formation of 
transient hairpins on the transposon ends and that piggyBac target joining 
occurs by the direct attack of the 3'OH transposon ends on to the target DNA. 
This is the same strategy for target joining used by the members of DDE 
superfamily of transposases and retroviral integrases. Analysis of mutant 
piggyBac transposases in vitro and in vivo using a piggyBac transposition system 
we have established in Saccharomyces cerevisiae suggests that piggyBac 
transposase is a member of the DDE superfamily of recombinases, an unanticipated 
result because of the lack of sequence similarity between piggyBac and DDE 
family of recombinases.