PBac{IT.GAL4} contains an enhancer trap cassette that consists of a minimal P\T promoter fused upstream of sequence encoding a GAL4 driver followed by the Hsp70 3' UTR. A loxP cassette containing the w+mC marker is present downstream of the enhancer trap cassette. An attP site is present upstream of the enhancer trap cassette; this attP site acts as a target site that allows the GAL4 enhancer trap cassette to be swapped with another cassette from any compatible InSITE donor construct (this process typically involves first excising the loxP cassette in the PBac{IT.GAL4} target element, then using phiC31:int integrase to insert the new donor cassette into the attP site, and finally completing the swap by using P1cre recombinase to remove the original target GAL4 coding region).