A single loxP site and an frt flanked neomycin resistance cassette were inserted upstream of exon 4 and a second loxP site was inserted downstream of the exon. Neomycin was excised in mice by crossing to the FLP deleter line, Tg(ACTFLPe)9205Dym. Deletion of exon 4 by cre mediated excision will result in a frameshift and a premature stop codon in exon 5. (J:159448)