3HCL:
reference: A geometric approach to the crystallographic solution of nonconventional DNA structures: helical superstructures of d(CGATAT)., Martinez de Ilarduya I, De Luchi D, Subirana JA, Campos JL, Uson I, Angew Chem Int Ed Engl. 2010 Oct 18;49(43):7920-2. PMID: 20848628

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