1GPP:
reference: High resolution crystal structure of domain I of the Saccharomyces cerevisiae homing endonuclease PI-SceI., Werner E, Wende W, Pingoud A, Heinemann U, Nucleic Acids Res 2002 Sep 15;30(18):3962-71. PMID: 12235380

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