CAR, (MB67; NR1I3) is a 40 kDa member of the NR1 subfamily of the nuclear hormone receptor family. CAR is predominantly expressed in the liver and forms a heterodimer with RXR. The CAR/RXR heterodimer activates retinoic acid, xenobiotic and phenobarbital response elements. There are two isoforms of the CAR nuclear hormone receptor. Each contains a DNA-binding hinge and dimerization domain. One is full-length at 352 amino acids while the other shows a 4 amino acid truncation at the extreme C-terminus.