The P{EP(-loxP)y+.UAS} element is generated in vivo by excision of the loxP cassette from P{EP(loxP.UAS)y+.UAS}. It contains UAS regulatory sequences at its 3' end, oriented so that in the presence of a GAL4 driver, transcription from UAS is directed outwards from this end of the element. A single loxP site is present upstream of the UAS sequences.