Movie S8.

Processive elongation and streptavidin-induced filament trapping on the carbon-coated glass surface. In the movie, text of “+SA” is displayed when 5 nM streptavidin is added in the sample. Subsequently, text of “washout methylcellulose” is displayed when methylcellulose is washed out by –MC basic buffer containing G-actin and profilin. After washout of methylcellulose, F-actin trapped by streptavidin remains on the carbon-coated glass surface. Time is in seconds. Scale bar, 20 μm.