Figure 4B(1). Five protein families dictate different transposition pathways: DDE-transposases, reverse transcriptase/endonucleases (RT/En), tyrosine (Y)-transposases, serine (S)-transposases and rolling-circle (RC)- or Y2-transposases. Transposons (blue) can be either 'cut-out' or 'copied-out' of the flanking donor DNA (green). a | Most DDE-transposons excise from the flanking DNA to generate an excised linear transposon, which is the substrate for integration into a target (orange). b | Retrotransposons copy-out by reverse-transcribing (RT) a full-length copy of their RNA (purple) that is generated by transcription (Txn). Long-terminal repeat (LTR)-retrotransposons make a full-length cDNA copy (pink represents newly replicated DNA) from their RNA and integrate this into a target using a DDE-transposase. c | TP-retrotransposons use reverse transcriptase (RT) to copy their RNA directly into a target that has been nicked by a transposon-encoded nuclease (En). d | Y-retrotransposons are thought to generate a circular cDNA intermediate by reverse transcription. A Y-transposase integrates the element into the target. e | and f | Y- and S-transposons encode either a tyrosine or serine transposase, which mediates excision of the transposon to form a circular intermediate. A reversal of the catalytic steps results in transposon insertion. g | Y2-transposons 'paste' one strand of the transposon into a target and use it as a template for DNA replication. Two models have been proposed for Y2-transposition. Representatives of each type of transposon are listed below each pathway (Curcio and Derbyshire 2003). Reproduced with permission from Nature Publishing Group.
Curcio, M. J. and K. M. Derbyshire (2003). "The outs and ins of transposition: from mu to kangaroo." Nat Rev Mol Cell Biol 4(11): 865-877. http://www.ncbi.nlm.nih.gov/pubmed/14682279.