3RTX:
reference: Structural insights to how mammalian capping enzyme reads the CTD code., Ghosh A, Shuman S, Lima CD, Mol Cell. 2011 Jul 22;43(2):299-310. Epub 2011 Jun 16. PMID: 21683636

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