Electron micrograph of negatively stained protofilaments assembled in vitro from E. coli FtsZ (1 μM FtsZ, 50 mM MES [morpholineethanesulfonic acid] [pH 6.5], 100 mM KAc, 5 mM MgAc, 1 mM GTP). Electron micrograph of negatively stained protofilaments assembled in vitro from E. coli FtsZ (1 μM FtsZ, 50 mM MES [morpholineethanesulfonic acid] [pH 6.5], 100 mM KAc, 5 mM MgAc, 1 mM GTP). The bar is 100 nm. This specimen was prepared on a carbon film treated with UV light and ozone to render it hydrophilic (24). With these carbon films we obtain protofilaments at lower FtsZ concentrations, and they are longer than those previously reported. The protofilaments here are mostly straight, but some show a tendency to curve. Harold P. Erickson et al. Microbiol. Mol. Biol. Rev. 2010; doi:10.1128/MMBR.00021-10