A cassette containing a bcl2 splice acceptor (SA) and a FRT-flanked beta-geo gene was inserted into the PvuII site upstream of exon 2. A loxP site was included upstream of the cassette and another loxP site was inserted into the BglII site in intron 3. Cre-mediated recombination removed the beta-geo reporter and exon 2. (J:189192)