Within the text, corrected words are highlighted.
The quality of Figure 1A was rather bad. The contrast was corrected and a new figure was inserted. In the new Figure 1A, the sheath is quite visible. The quality of EM figure is very low as embedded in an MS word file. We provide a better quality figure as supplemental Figure S1. The use of “sheath” is therefore correct in the paragraph describing the figure. In the model, the word “sliding” was not understood in the sense in which we wanted it to be. This is lateral sliding that provokes curvature of the filament. This point was clarified in the text.