1WRS:
reference: Refined solution structures of the Escherichia coli trp holo- and aporepressor., Zhao D, Arrowsmith CH, Jia X, Jardetzky O, J Mol Biol 1993 Feb 5;229(3):735-46. PMID: 8433368

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