P{(-FRT)lacZ.UAS.T7.FRT} is an enhancer trap construct generated in vivo by excision of the 5' FRT cassette (containing the homing fragment and ry+t7.2 marker) from the P{FRT(HF.ry+)lacZ.UAS.T7.FRT} element. The 3' FRT cassette remains, containing: 1: UAS regulatory sequences (with a minimal TATA promoter) fused upstream of sequence encoding a lacZ reporter, 2: two tandem 49bp T7\RpT7 promoters (oriented towards the outside of the element). The construct is designed to study DNA accessibility, which can be assayed by measuring 1: activation of the UAS-lacZ reporter by a GAL4 driver 2: transcription by T7 RNA polymerase from the T7\RpT7 promoters and 3: excision of the FRT cassette(s) by FLP recombinase. In the absence of a GAL4 driver, the construct can also act as an enhancer trap, with expression of the lacZ reporter being influenced by neighbouring enhancer sequences (the expression may also be influenced in a negative manner by genomic silencing sequences).
The Scer\FRT cassette containing HF-BXC6.7 and ry+t7.2 has been excised. Ecol\lacZHF.Scer\UAS and two tandem 49bp T7 promoters (oriented towards the outside of the P-element) followed by a Scer\FRT site remain.