2KUZ:
reference: 2-Aminopurine Incorporation Perturbs the Dynamics and Structure of DNA., Dallmann A, Dehmel L, Peters T, Mugge C, Griesinger C, Tuma J, Ernsting NP, Angew Chem Int Ed Engl. 2010 Jul 14. PMID: 20632340

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