説明
Publisher Summary This chapter describes the expression cloning of ligand biosynthetic enzymes. Endogenous ligands for steroid and vitamin D nuclear receptors are synthesized from cholesterol by specific converting enzymes expressed in multiple tissues. Many of the enzymes involved in ligand biosynthesis are the members of the cytochrome P450 family. Those enzymes that perform the final conversion of ligands into their active forms are thought to play crucial roles in target tissues. The expression assay is based on the observation that nuclear receptors are activated by their cognate ligands, but not by their precursors or metabolites. Expression-cloning method, which relies on the conversion of a precursor into the active form of a ligand, is in principle applicable to the isolation of other biosynthetic enzymes. The only requirement for success is that the activity of the ligand produced in the transfected cells must be higher than its precursor in terms of its transactivation function for the nuclear receptor.