1CKI:
reference: Three-dimensional structure of mammalian casein kinase I: molecular basis for phosphate recognition., Longenecker KL, Roach PJ, Hurley TD, J Mol Biol 1996 Apr 5;257(3):618-31. PMID: 8648628

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