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. Exon 4 and the neomycin resistance cassette were excised in mice by crossing to the cre deleter line, Tg(CMV-cre)1Cgn. Deletion of exon 4 results in a frameshift and a premature stop codon in exon 5. (J:159448)