[Transcriptional control by steroid receptor].
Nuclear receptors for steroid/thyroid hormones, vitamin A,D and fat-soluble ligands form a gene superfamily of ligand-inducible transcription factors, which plays an important roles in a wide spectrum of biological events by regulating expression of a set of target genes. Two domains (A/B and E) of nuclear receptors are demonstrated to activate transcription, designated AF-1 (A/B) and AF-2 (E), respectively. Homo- and hetero-dimers of nuclear receptors bind target enhancer elements in the target gene promoters. The target enhancer elements are referred as hormone response elements (HRE), and composed of two hexamer core motifs. The orientations and spaces between two core motifs play critical roles in discreminating the recognition of HREs among the members of nuclear receptor. DNA-bound nuclear receptors controls transcription in a ligand-binding dependent way in co-operation with a multiprotein complex containing RNA polymerase II and a series of auxiliary factors, TFIIA,B,D, E,F and H. During process of ligand-induced transactivation by nuclear receptors, nuclear co-factors interacting with the AF-1 and AF-2 seem to be involved. Several transcriptional co-activators and co-repressors have been recently identified, and their function is currently under investigation.