The assembly of SyFtsZ assayed by light scattering shows two stages in HMK buffer at pH 7.5 (A and B).
A shows that light scattering reaches a final plateau at 300–600 s. B amplifies the first 100 s and shows that light scattering first approaches an intermediate plateau at 30–50 s and then accelerates to the much higher final plateau. Note that light scattering does not measure polymer, but is greatly enhanced by bundling. The signal here is primarily a measure of bundle formation. C and D, EM of 10 μm SyFtsZ shows short single pfs and partial circles at the first stage assembly, at 30 s (C), and assembly into straight bundles and toroids at the second stage of assembly, at 300 s (D). Bar, 200 nm. E, light-scattering assay of 10 μm SyFtsZ in HMK buffer assembled in 0.1 mm GTP. Light scattering reached a plateau at 500 s and then slowly decreased to the base after 1 h. F, the GTPase activity of SyFtsZ in HMK buffer was 0.41 ± 0.2 GTP/min/FtsZ above a critical concentration of 1.6 μm. Error bars, S.D.