The targeting vector was designed (by site-directed mutagenesis) to substitute a serine to histidine at amino acid position 270 and leucine to alanine at amino acid position 277 of exon 9. An FRT-flanked neomycin cassette was inserted upstream of exon 9. Chimeric animals were crossed to C57BL/6J and the F1 progeny crossed to B6.Cg-Tg(ACTFLPe)9205Dym/J (actin-FLPe) to remove the neo cassette and leave a single FRT site upstream of exon 9. (J:144692)