DNA-binding domain of retinoic acid receptor (RAR) is composed of two C4-type zinc fingers
DNA-binding domain of retinoic acid receptor (RAR) is composed of two C4-type zinc fingers. Each zinc finger contains a group of four Cys residues which co-ordinates a single zinc atom. RAR interacts with specific DNA sites upstream of the target gene and modulates the rate of transcriptional initiation. RARs mediate the biological effect of retinoids, including both natural dietary vitamin A (retinol) metabolites and active synthetic analogs. Retinoids play key roles in a wide variety of essential biological processes, such as vertebrate embryonic morphogenesis and organogenesis, differentiation and apoptosis, and homeostasis. RAR function as a heterodimer with retinoic X receptor by binding to specific RAR response elements (RAREs), which are composed of two direct repeats of the consensus sequence 5'-AGGTCA-3' separated by one to five base pair and found in the promoter regions of retinoid target genes. Like other members of the nuclear receptor (NR) superfamily of ligand-activated transcription factors, retinoic acid receptors have a central well conserved DNA binding domain (DBD), a variable N-terminal domain, a non-conserved hinge and a C-terminal ligand binding domain (LBD).