The P{XP-U} transgene represents the transgenic element generated in vivo when FLP is used to induce recombination between the FRT sites of two insertions of the P{XP} transgene. P{XP-U} contains (from 5' to 3'): a single FRT site, the w^+mC marker, a gypsy insulator sequence and UAS regulatory sequences. The UAS sequences are oriented outwards, so in that the presence of a GAL4 driver, transcription from UAS is directed outwards from the 3' end of the element, potentially driving overexpression of any nearby genomic loci. P{XP-U} is typically generated as part of a deletion-generation strategy; when the two insertions are in trans and are in the appropriate relative orientation, FLP-mediated recombination can result in deletion of the genomic region between the two original insertions along with production of the P{XP-U} element at the recombination point.