1PK3:
reference: Structural organization of a Sex-comb-on-midleg/polyhomeotic copolymer., Kim CA, Sawaya MR, Cascio D, Kim W, Bowie JU, J Biol Chem. 2005 Jul 29;280(30):27769-75. Epub 2005 May 19. PMID: 15905166

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