Electron microscopic images of rotary-shadowed octamers of AMII constructs. To maximize octamer formation, WT, S639D, 4S/A, and ∆NHT were polymerized in 10 mM imidazole (pH 7.0), 2.5 mM KCl, 1 mM ATP, and 1 mM MgCl2, and pWT, pS639D, and 4S/E were polymerized in 10 mM imidazole (pH 7.0), 2.5 M KCl, 1 mM ATP, and 2 mM MgCl2. The bare zones are longer and the heads more tightly clustered in pWT, pS639D, and 4S/E than in WT, S639D, and 4S/A (Table 2). Panels are labeled as in Fig. 3. (Scale bar, 100 nm.)