2KM3:
reference: Sequence variant (CTAGGG)n in the human telomere favors a G-quadruplex structure containing a G.C.G.C tetrad., Lim KW, Alberti P, Guedin A, Lacroix L, Riou JF, Royle NJ, Mergny JL, Phan AT, Nucleic Acids Res. 2009 Oct;37(18):6239-48. Epub 2009 Aug 19. PMID: 19692585

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