2H1O:
reference: Structure of FitAB from Neisseria gonorrhoeae bound to DNA reveals a tetramer of toxin-antitoxin heterodimers containing pin domains and ribbon-helix-helix motifs., Mattison K, Wilbur JS, So M, Brennan RG, J Biol Chem. 2006 Dec 8;281(49):37942-51. Epub 2006 Sep 18. PMID: 16982615

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