UAS regulatory sequences followed by 2kb spacer sequence from the Ecol\lacZ gene are fused upstream of a promoterless w minigene that lacks the endogenous Wari insulator that is normally located on the 3' side of the w transcription unit. A loxP cassette containing a transcriptional terminator derived from the regulatory region of the Achaete-Scute gene complex has been inserted in the spacer sequence. A y+t* marker is present downstream of the w minigene.