The P{GSV7} element contains UASt regulatory sequences at its 5' end, oriented so that in the presence of a GAL4 driver, transcription from UASt is directed outwards from this end of the element. This can result in misexpression of neighbouring genomic loci when the element is inserted in the genome. The element also contains a w^+mGS marker. A pair of loxP sites have been inserted immediately inside the P-element termini, in inverted orientation with respect to each other. P1cre can be used to catalyze recombination between these loxP sites, which results in inversion of the intervening sequence, reversing the directionality of the misexpression driven from the UASt sequences.