3K1V:
reference: Cocrystal structure of a class I preQ1 riboswitch reveals a pseudoknot recognizing an essential hypermodified nucleobase., Klein DJ, Edwards TE, Ferre-D'Amare AR, Nat Struct Mol Biol. 2009 Mar;16(3):343-4. Epub 2009 Feb 22. PMID: 19234468

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