1CKN:
reference: X-ray crystallography reveals a large conformational change during guanyl transfer by mRNA capping enzymes., Hakansson K, Doherty AJ, Shuman S, Wigley DB, Cell 1997 May 16;89(4):545-53. PMID: 9160746

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