P{CR2} is designed for use in an enhancer-blocking assay, which can be used to define and characterize chromatin domain boundary elements. It contains two divergently transcribed reporters: Adh and lacZ, with the complete Yp1-Yp2 intergenic region (extends from +37bp relative to the Yp1 transcription start site through to +105bp relative to the Yp2 transcription start site) fused between the reporters such that the Yp1 promoter is proximal to Adh and the Yp2 promoter is proximal to lacZ. Sequence to be tested for enhancer-blocking activity can be inserted into the Yp1-Yp2 intergenic region.