A loxP site was inserted upstream of the exon encoding the carboxy terminus of the first PDZ domain and the amino terminus of the second PZD domain and an FRT-flanked neomycin resistance cassette with a 3' loxP site was inserted downstream of this exon. Flp-mediated recombination was used to remove the selection cassette. Cre-mediated recombination removed the exon. (J:202688)