5K8H:
reference: Crystal structure of a poly(rA) staggered zipper at acidic pH: evidence that adenine N1 protonation mediates parallel double helix formation., Gleghorn ML, Zhao J, Turner DH, Maquat LE, Nucleic Acids Res. 2016 Jun 10. pii: gkw526. PMID: 27288442

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