4U9M:
reference: Structure of the DNA Duplex d(ATTAAT)2 with Hoogsteen Hydrogen Bonds., Acosta-Reyes FJ, Alechaga E, Subirana JA, Campos JL, PLoS One. 2015 Mar 17;10(3):e0120241. doi: 10.1371/journal.pone.0120241., eCollection 2015. PMID: 25781995

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