P(GAL4)

Synthetic P element of Drosophila melanogaster, comprising long-terminal repeats flanking a mini-white gene to mark flies carrying the P element by their red eye colour, Bluescript to allow plasmid rescue of DNA flanking the genomic insertion site, and a gene encoding the yeast transcription factor GAL4, downstream of a weak (permissive) promoter. Although itself unable to move within the genome, P(GAL4) mobilization can be induced by crossing in a source of transposase. Patterns of expression of neighbouring genes can be detected (see enhancer trapping) by crossing in a reporter gene (e.g. lacZ, green fluorescent protein (GFP) ) under the control of the UAS promoter recognized by GAL4.