2FKD:
reference: The structural basis of cooperative regulation at an alternate genetic switch., Pinkett HW, Shearwin KE, Stayrook S, Dodd IB, Burr T, Hochschild A, Egan JB, Lewis M, Mol Cell. 2006 Mar 3;21(5):605-15. PMID: 16507359

This OCA Structure page
uses Jmol, developed by the Jmol Development Team (documentation).