1FG1:
reference: Does a single metal ion bridge the A-9 and scissile phosphate groups in the catalytically active hammerhead ribozyme structure?, Murray JB, Scott WG, J Mol Biol 2000 Feb 11;296(1):33-41. PMID: 10656816

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