Synchrotron SAXS data from solutions of the Rel Homology Domain of p50/RelA bound to IFN kB site DNA in 25 mM Tris.Cl, 150 mM NaCl, 1 mM DTT, 0.5 mM EDTA, pH 7.5 were collected on the 12.3.1 (SIBYLS) beam line at the Advanced Light Source (ALS; Berkeley, CA, USA) using a Pilatus3 X 2M detector at a sample-detector distance of 2 m and at a wavelength of λ = 0.127 nm (I(s) vs s, where s = 4πsinθ/λ, and 2θ is the scattering angle). Solute concentrations ranging between 1.3 and 5 mg/ml were measured at 10°C. 50 successive 15 second frames were collected. The data were normalized to the intensity of the transmitted beam and radially averaged; the scattering of the solvent-blank was subtracted. The low angle data collected at lower concentration were merged with the highest concentration high angle data to yield the final composite scattering curve.