Fig. 3. (A) ParM polymers visualized by electron microscopy. Typical ParM filaments formed by incubation in 30 mM Tris–HCl pH 7.5, 100 mM KCl, 2 mM MgCl₂, 1 mM DTT and 2 mM ATP-γ-S. Filament formation required Mg²⁺ and occurred in the presence of ATP or its non-hydrolysable analogue, ATP-γ-S, but not in the presence of ADP. Polymers have a cross-sectional diameter of ∼7 nm. Scale bar: 50 nm. (B) Nucleotide-dependent polmerization of ParM. Polymerization of 10 µM ParM was assayed in 30 mM Tris–HCl pH 7.5, 100 mM KCl and 1 mM DTT. MgCl₂ (2 mM), EDTA (10 mM) and nucleotides (2 mM) were added as indicated. The protein was centrifuged immediately after mixing at 100 000 g for 15 min at ambient temperature. Supernatant and solubilized pellets were analysed by SDS–PAGE and Coomassie Blue staining.