1D4R:
reference: The 2 A structure of helix 6 of the human signal recognition particle RNA., Wild K, Weichenrieder O, Leonard GA, Cusack S, Structure Fold Des 1999 Nov 15;7(11):1345-52. PMID: 10574798

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