156D:
reference: Refined solution structure of the dimeric quadruplex formed from the Oxytricha telomeric oligonucleotide d(GGGGTTTTGGGG)., Schultze P, Smith FW, Feigon J, Structure 1994 Mar 15;2(3):221-33. PMID: 8069635

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