2WAQ:
reference: Evolution of Complex RNA Polymerases: The Complete Archaeal RNA Polymerase Structure., Korkhin Y, Unligil UM, Littlefield O, Nelson PJ, Stuart DI, Sigler PB, Bell SD, Abrescia NG, PLoS Biol. 2009 May 5;7(5):e102. PMID: 19419240

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