Figure 5. Schematic comparing organization of the related archaellum and type IVa pilus basal bodies. In the bacterial T4P (B), an integrated system of components spanning the outer and inner membranes (OM, IM) uses the peptidoglycan cell wall (PG) to clamp the ATPase, allowing rotation of PilC (orange) in the membrane to assemble the pilus fiber. In the T. kodakaraensis archaellum (A), our results suggest that an integrated system of components extends from the single membrane (CM) inward to a large conical structure in the cytoplasm to similarly brace the ATPase. Sensory components (purple) are proposed to be located in the periplasm for the T4P (integrating signals for disassembly) and the cytoplasm for the archaellum (integrating signals for rotation). 