Li, X. et al. Proc. Natl. Acad. Sci. USA 110, E2279–E2287 (2013).

An attractive feature of the piggyBac system is that the transposon can be seamlessly excised from the genome; this system is therefore particularly useful as a vehicle for transient transgene expression. However, a substantial fraction of excised transposons reintegrate into the genome. Li et al. have now developed an excision-competent, integration-defective piggyBac transposase. Combining alanine-scanning mutagenesis of active-site residues with other known and newly identified mutants that modulate transposase activity, they generated transposase variants that are hyperactive at excision but lack integration activity in mammalian cells. Fusion to zinc-finger proteins that bind specific DNA sequences could rescue the integration activity of some variants, but not in a targeted fashion.