1NYD:
reference: Association of DNA quadruplexes through G:C:G:C tetrads. Solution structure of d(GCGGTGGAT)., Webba da Silva M, Biochemistry 2003 Dec 16;42(49):14356-65. PMID: 14661946

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