Protein DNA Assemblies. (a) Structure of DNA binding domain and operator DNA (Osym). (b) Wild-type operator DNA (O1) and auxiliary operators O2 and O3. O1, O2, O3, and Osym all assemble with wild-type the DNA binding domain D1. Variations of operator DNA (OS2, OS3, OS4, and OS5) assemble with orthogonal DNA binding domains (DS2, DS3, DS4, and DS5).