RQCD1, also known as RCD1, is a novel transcriptional cofactor that mediates retinoic acid-induced cell differentiation. It down-regulates MYB- and JUN-dependent transcription and may play a role in cell differentiation. RQCD1 also plays a role in retinoic acid-controlled lung development. Recombinant human RQCD1 protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.