The PBac{WH} element contains UAS regulatory sequences at its 5' end, oriented so that in the presence of a GAL4 driver, transcription from UAS 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. In addition it contains a long (199bp) FRT site, a w^+mC marker and a gypsy insulator sequence (at the 3' end of the element, downstream of the marker allele).

A diagram of the PBac{WH} element is available at the [GDP Transposons page](http://flypush.imgen.bcm.tmc.edu/pscreen/transposons.html)