A loxP site was inserted in intron 4 and an FRT flanked PGK-neomycin selection cassette folled by a second loxP site was inserted in the 3' untranslated region of exon 6. The selection cassette was subsequently removed by flp expression. Exons 5 and 6 were deleted in the germline via Cre-mediated recombination. (J:192725)