Structure of NF-κB p50 homodimer bound to a κB site

The 2.3-Â crystal structure of the transcription factor NF-κB p50 homodimer bound to a palindromic κB site reveals that the Rel homology region folds into two distinct domains, similar to those in the immunoglobulin superfamily. The p50 dimer envelopes an undistorted B-DNA helix, making specific contacts along the 10-base-pair κB recognition site mainly through loops connecting secondary structure elements in both domains. The carboxy-terminal domains form a dimerization interface between β-sheets using residues that are strongly conserved in the Rel family.