1DNS:
reference: Base only binding of spermine in the deep groove of the A-DNA octamer d(GTGTACAC)., Jain S, Zon G, Sundaralingam M, Biochemistry 1989 Mar 21;28(6):2360-4. PMID: 2730868

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