A site 5' of the Ubb gene was targeted with a construct composed of a CMV/beta-actin enhancer and promoter (CAG), a floxed beta-geo with three transcription termination sites and an Edn2 and IRES-GFP. Cre-mediated excision of the floxed beta-geo construct is required to achieve expression of the Edn2 and GFP cassette. (J:201133)