Fig 4. Steady-state treadmilling and chirality of FtsZ vortices: Dependence on GTPase activity and location of the mts.

(A-C) Left panels: Representative snapshots of the rings formed upon addition of GTP (4 mM) and Mg²⁺ (5 mM) by (A) FtsZ-YFP-mts, whose mts is located at the C-terminus of FtsZ; (B) mts-H-FtsZ-YFP, with mts located at the N-terminus of FtsZ; and (C) FtsZ*[T108A]-YFP-mts, a variant of FtsZ-mts with diminished GTPase activity. Right panels: Kymograph analysis showing (A) a positive slope that corresponds to the apparent clockwise rotation time of the selected ring (red circle); (B) a negative slope that corresponds to an apparent counterclockwise rotation, indicating that the position of the mts determines the chirality of the apparent rotation; (C) no apparent slope corresponding to static rings, suggesting that the apparent rotation in (A) and (B) is mediated by GTP hydrolysis. (D) Velocity distributions for FtsZ-YFP-mts (red) and mts-H-FtsZ-YFP (blue) with mean rotational speed values of 34 nm/s and 25 nm/s, respectively. Further details under Materials and methods and Results. GTP, guanosine triphosphate; mts, membrane-targeting sequence; YFP, yellow fluorescent protein.