A cassette containing a loxP site, duplicated exon 12, and a neo cassette with 3 polyadenylation sequences and a 3' loxP site was inserted upstream of exon 12. An IRES, nuclear localization sequence, and lacZ gene with a polyadenlylation sequence were inserted downstream of exon 12. Cre-mediated recombination removed the neo/STOP cassette. (J:174591)