1HC8:
reference: A compact RNA tertiary structure contains a buried backbone-K+ complex., Conn GL, Gittis AG, Lattman EE, Misra VK, Draper DE, J Mol Biol 2002 May 10;318(4):963-73. PMID: 12054794

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