MRC Laboratory of Molecular Biology, Cambridge, UK.
Steroid hormone receptors control gene expression through binding, as dimers, to short palindromic response elements located upstream of the genes they regulate. An independent domain of approximately 70 amino acids directs this sequence-specific DNA binding and is highly conserved between different receptor proteins and related transcription factors. This domain contains two zinc-binding Cys2-Cys2 sequence motifs, which loosely resemble the 'zinc-finger' motifs of TFIIIA. Here we describe the structure of the DNA-binding domain from the oestrogen receptor, as determined by two-dimensional 1H NMR techniques. The two 'zinc-finger'-like motifs fold to form a single structural domain and are thus distinct from the independently folded units of the TFIIIA-type zinc fingers. The structure consists of two helices perpendicular to each other. A zinc ion, coordinated by four conserved cysteines, holds the base of a loop at the N terminus of each helix. This novel structural domain seems to be a general structure for protein-DNA recognition.