||Liver X Receptors (LXRs) are nuclear receptors that regulate the metabolism of cholesterol and bile acids. There are two subtypes of LXRs, LXRα and LXRβ. LXRα is preferentially expressed in liver, small intestine, kidney and spleen. In contrast, LXRβ expression is ubiquitous. The genomic structure and the promoter regions of the two LXR genes contain specific regulatory sites, which suggest that LXRs may have physiological roles in the immune system. Like other nuclear receptors, LXRs heterodimerize with Retinoid X Receptor (RXR) for function. LXRs are activated by naturally occurring oxysterols and regulate the expression of target genes, including ATP binding cassette transporter 1 (ABC1), ATP binding cassette transporter 8 (ABC8) and cholesterol ester transfer protein (CETP). LXRβ expressed in livers of LXRα knockout mice does not compensate for the loss of LXRα. In addition, LXRβ, but not LXRα, is also able to activate transcription of a reporter gene, which contains a specific direct repeat separated by 1 bp (DR1) element in the promoter, suggesting that LXRβ may have different biological functions. Recombinant LXR is isolated from anE. colistrain that carries the coding sequence of the human LXR from amino acids 211-461 under the control of a T7 promoter.