Nuclear receptors are organized into distinct functional domains, of which the most conserved is a 66-amino-acid DNA-binding domain (DBD) (1). This region, in some cases together with its C-terminal extension into the hinge region, imparts the receptor's ability to bind to target DNA sequences and form the appropriate cooperative homodimeric or heterodimeric complexes (2 -6 ). Important advances in understanding DNA recognition has come from the direct visualization of the protein-DNA complexes, which can be achieved through X-ray diffraction studies ((7 -12 ), as well as through other structural and biophysical methods that directly probe the DNA-binding surface of nuclear receptors (13 -(17 ).
