Use of the piggyBac transposon system to disrupt gene function and 'trap' promoter elements. The piggyBac transposase encoded by the pHTH plasmid can integrate a gene cassette (carried on the pBAC-BACII-GFP-hDHFR plasmid) flanked by piggyBac-specific inverted repeats into random TTAA sites within the P. berghei genome . The gene cassette contains a promoter-less green fluorescent protein (gfp) gene and a human dihydrofolate reductase (hdhfr) selectable marker. The function of P. berghei genes can be ablated by disrupting their coding sequences or their promoters by insertion of the gfp-hdhfr cassette. If the cassette inserts downstream of a gene promoter (as shown here) this promoter can drive expression of gfp, which provides information about the timing of expression of the disrupted gene.