2K9M:
reference: Structure of the RNA Polymerase Core-Binding Domain of sigma(54) Reveals a Likely Conformational Fracture Point., Hong E, Doucleff M, Wemmer DE, J Mol Biol. 2009 May 5. PMID: 19426742

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