4CKC:
reference: Crystal structure of vaccinia virus mRNA capping enzyme provides insights into the mechanism and evolution of the capping apparatus., Kyrieleis OJ, Chang J, de la Pena M, Shuman S, Cusack S, Structure. 2014 Mar 4;22(3):452-65. doi: 10.1016/j.str.2013.12.014. PMID: 24607143

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