||Retinoic acid receptors are important in the regulation of growth and differentiation of epithelial tissues, embryonic and central nervous system development and hematopoiesis. Retinoids mediate their effect by two classes of nuclear receptor proteins, the Retinoic Acid Receptors (RARs) and the Retinoid X Receptors (RXRs), that each consist of three isotypes (α,β, and γ) encoded in separate genes. Upon dimerization with RXR, RARs can bind to specific enhancer sequences in the DNA, so-called Retinoic Acid Response Elements (RAREs), resulting in transcriptional activation of target genes in the presence of ligand. Retinoids, the natural and synthetic vitamin A derivatives, are known to inhibit the proliferation of lung cancer and breast cancer cells and the growth of carcinogen-induced bronchogenic squamous cell carcinoma and mammary tumors, and have been used as chemoprevention agents against both types of cancer. A growing body of evidence supports the hypotheses that the RARβ gene is a tumor suppressor gene and the chemopreventive effects of retinoids are due to induction of RARβ. RARβ expression is reduced in many malignant tumors including breast carcinoma. Recombinant RAR β-LBD was expressed in a baculovirus system and purified by an affinity column in combination with FPLC chromatography.