(A) Schematic showing the topology of receptor-trimers-of-dimers (purple), CheA (domains P1–P4 light gray/dark gray indicating domains in each CheA monomer, domain P5 orange), and CheW (blue) in membrane-bound arrays. The methylation region of each receptor dimer is indicated by a pink star. IM = inner membrane. (B) Top-view of the arrangement of the array components showing the interaction sites between the receptors, CheA and CheW, colored as in (A). (C) Schematic showing the topology of receptor, CheA, and CheW complexes in cytoplasmic arrays, colored as in (A). Cytoplasmic chemoreceptors assemble into two hexagonally packed arrays interacting at their presumably ligand-binding tips.