3I4H:
reference: Cas6 is an endoribonuclease that generates guide RNAs for invader defense in prokaryotes., Carte J, Wang R, Li H, Terns RM, Terns MP, Genes Dev. 2008 Dec 15;22(24):3489-96. PMID: 19141480

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