Exon 8 was replaced with a loxP site, a modified exon 8 with nucleotide substitutions that result in the amino acid substitution of leucine for arginine at position 218 (R218L), and an FRT-flanked neo cassette with a 3' loxP site. Cre-mediated recombination removed the neo cassette leaving the modified exon 8 floxed. (J:169475)