Mice with a targeted deletion of the last exon encoding the ligand binding domain and all of the 3' untranslated region were produced as follows: A loxP site was inserted in the intron 5' to the last exon and a loxP-flanked neomycin cassette was inserted 3' to the last exon. After production of chimeric founder mice, F1 mice were mated to Tg(EIIa-Cre)1Lmgd mice to produce offspring that carried a recombined deletion of the last exon and neomycin cassette. No Nr1h4 protein product is detected in liver tissue from these null mice although an aberrant transcript appears to be generated. (J:64792)