A loxP site was inserted into intron 4 and a second loxP site and an FRT site flanked neomycin resistance gene cassette into intron 5. The neo cassette was deleted through subsequent flp-mediated recombination. Floxed exon 5 was removed through subsequent cre-mediated recombination. The expression of transcript from this allele is reduced 15-fold. (J:268582)