Exons 3 and 4 and were replaced with a universal docking site cassette. The cassette is composed of a splice acceptor IRES-Beta geo-lacZ sequence, a loxP site, followed by the deltaTK and neomycin under the control of the human beta-actin promoter, a second loxP site, a PhiC31 attP site and a puromycin sequence that is not active unless a promoter is inserted by PhiC31 at the attP site. (J:270051, J:290434)