A loxP site was inserted downstream of exon 9 and exon 11 was replaced with one containing nucleotide substitutions that result in the amino acid substitution of glutamic acid for tyrosine at position 672 (Y672E). An additional loxP site was inserted downstream of exon 12. An FRT flanked neo cassette inserted downstream of the modified exon 11 was removed by flp mediated recombination leaving exon 10, the modified exon 11, and exon 12 floxed.