CTL affects lateral interaction between FtsZ protofilaments. Electron micrographs of polymers formed by FtsZ CTL variants spotted on grids 15 min after addition of GTP and stained with uranyl formate. A, 8 μm FtsZ CTL variant with 2 mm GTP, 50 mm KCl, and 2.5 mm MgCl2. B, 4 μm FtsZ CTL variant with 2 mm GTP, 50 mm KCl, and 10 mm MgCl2. C, low magnification micrographs of FtsZ or ΔCTL polymers with 2 mm GTP, 50 mm KCl, and 10 mm MgCl2. D, 4 μm FtsZ CTL variant with 2 mm GTP, 50 mm KCl, and 2.5 mm MgCl2. Scale bars, 100 nm. *, single protofilaments; arrow, two- or three-filament bundles; #, multifilament bundles.