| 3PO2: reference: Structural basis of RNA polymerase II backtracking, arrest and reactivation., Cheung AC, Cramer P, Nature. 2011 Mar 10;471(7337):249-53. Epub 2011 Feb 23. PMID: 21346759 |
This OCA 
Structure page
uses Jmol,
developed by the Jmol Development Team
(documentation).