FtsZ, ZapA, and ZapB form long cable-like structures in vitro. Electron microscopy images of uranyl acetate-stained filaments and bundles. Polymerization reactions were performed at pH 6.5 as described in Materials and Methods. Using high (8.3 μM) or low (2 μM) concentrations of ZapB did not change the morphology of the structures formed. (A) ZapB (4.1 μM). Black arrows, thin ZapB filaments. (B) FtsZ (8.3 μM) and ZapA (3.2 μM). (C) ZapB (3.2 μM) and ZapA (3.2 μM). (D) FtsZ (8.3 μM) and ZapB (2 μM). Black arrows, FtsZ protofilaments. (E) FtsZ (8.3 μM), ZapA (3.2 μM), and ZapB(S4A L5A) (2 μM). Black arrow, array of parallel filaments. (F) FtsZ (8.3 μM), ZapA (3.2 μM), and ZapB (2 μM). Scale bar, 100 nm.