General organization and use of class II transposable elements as gene vectors. (A) Autonomous transposable elements consist of terminal inverted repeats (TIR; black arrows) that flank the transposase gene. (B) Bi-component transposon vector system for delivering transgenes that are maintained in plasmids. One component contains a DNA of interest between the transposon TIRs carried by a plasmid vector, whereas the other component is a transposase expression plasmid, in which the black arrow represents the promoter driving expression of the transposase. (C) The transposon carrying a DNA of interest is excised from the donor plasmid and is integrated at a chromosomal site by the transposase.