2GRB:
reference: Crystal structure of an RNA quadruplex containing inosine tetrad: implications for the roles of NH2 group in purine tetrads., Pan B, Shi K, Sundaralingam M, J Mol Biol. 2006 Oct 20;363(2):451-9. Epub 2006 Aug 12. PMID: 16978642

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