Fig. 8: Order of assembly steps into bacterial F₁.

a As a first step α-subunits (light blue) and β-subunits (dark blue) form αβ heterodimers, which requires the presence of nucleotides and Mg²⁺. b As next step three of these heterodimer building blocks assemble pairwise to the central stalk γ (dark green). Only after the formation of the full hexameric head, the δ-subunit (yellow) is able to bind. The ε-subunit (light green) can join into the assembly process at all intermediate step en-route to the F₁ complex.