An FRP-flanked neomycin resistance cassette downstream of a loxP site was inserted into intron 11 and a second loxP site was inserted in to intron 14 via homologous recombination. Heterozygous mice were bred with Tg(CMV-cre)1Cgn carriers to excise exons 12-14. RT-PCR analysis indicated that no detectable transcript was expressed from this allele. (J:99711)