Fig. 7.

Electron microscopic images of negatively stained WT, pWT, and 4S/E as a function of MgCl₂ concentration. All constructs were polymerized in 10 mM imidazole (pH 7.0), 2.5 mM KCl, 1 mM ATP, and varied MgCl₂ concentrations as indicated in the figure. The minifilaments of all constructs aggregated laterally in 6 and 10 mM MgCl₂ to form thick filaments, but the heads of pWT and 4S/E are more clustered, and the bare zones are more distinct for WT than for pWT and 4S/E. (Scale bar, 100 nm.)