The targeting construct contains a loxP site inserted in the intron 5' to the last exon and a loxP-flanked neomycin cassette inserted 3' to the last exon. Germline Cre-mediated recombination removed the floxed neo cassette leaving the last exon floxed. The last exon encodes the ligand binding domain and all of the 3' untranslated region. (J:64792)