A FRT-LoxP-Neomycin-FRT-LoxP selection cassette was inserted downstream of exon 4 and the third single LoxP site was inserted upstream of exon 4. The region flanked by the second and third LoxP sites is approximately 569 bp. Exon 4 encodes amino acids 337-386 and deletion of this sequence results in the creation of a premature stop codon. The neomycin selection cassette was removed via FLP-mediated recombination, leaving loxP sites flanking exon 4. (J:259070)