4FM9:
reference: The Structure of DNA-Bound Human Topoisomerase II Alpha: Conformational Mechanisms for Coordinating Inter-Subunit Interactions with DNA Cleavage., Wendorff TJ, Schmidt BH, Heslop P, Austin CA, Berger JM, J Mol Biol. 2012 Dec 7;424(3-4):109-24. doi: 10.1016/j.jmb.2012.07.014. Epub 2012, Jul 25. PMID: 22841979

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