4HK1:
reference: Structure of PCNA from Drosophila melanogaster., Wang K, Shi Z, Zhang M, Cheng D, Acta Crystallogr Sect F Struct Biol Cryst Commun. 2013 Apr 1;69(Pt 4):387-92., doi: 10.1107/S1744309113004971. Epub 2013 Mar 28. PMID: 23545643

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