(a) Mock experiment in which 5 μM FtsZ is added to monolayers, but no FtsA was present; (b) 0.1 μM FtsA+5 μM FtsZ; (c) 0.5 μM FtsA+5 μM FtsZ; (d) 0.5 μM FtsA+5 μM FtsZ on a grid without a monolayer. (e–g) Same conditions as (c), showing examples of aligned unbundled FtsZ filaments (long arrows) on FtsA minirings merging with bundled FtsZ filaments not associated with visible FtsA minirings (short arrows). (h) A large swirl of aligned FtsZ filaments on FtsA minirings. ATP and GTP were added to all experiments. Scale bar, 100 nm.