Select examples of protein domains binding other macromolecules. (A) The PX domain of a yeast sorting nexin (orange) binding to the headgroup of a lipid, PtdIns3P (blue), PDB ID: 1OCU. (B) The glucocorticoid receptor, a homodimer, (purple, red) bound to a DNA molecule (tan helix), PDB ID: 1R4R. (C) The Trp RNA-binding attenuation protein (TRAP) (green) bound to an RNA molecule (pink helix), PDB ID: 1C9S.