3C9K:
reference: Histone octamer helical tubes suggest that an internucleosomal four-helix bundle stabilizes the chromatin fiber., Frouws TD, Patterton HG, Sewell BT, Biophys J. 2009 Apr 22;96(8):3363-71. PMID: 19383479

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