1S2R:
reference: High-resolution structure of an extended A-tract: [d(CGCAAATTTGCG)]2., Woods KK, Maehigashi T, Howerton SB, Sines CC, Tannenbaum S, Williams LD, J Am Chem Soc 2004 Dec 1;126(47):15330-1. PMID: 15563130

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