Fig. 4

Direct observation of individual Srv2/CAP molecules interacting with Cofilin-saturated actin filaments. a Representative step photobleaching traces for surface-adsorbed Cy5-Srv2ΔCARP molecules. One of the molecules photobleached in one step (red), and the other in two steps (black). Traces offset for clarity. Arrowheads denote photobleaching events. b Depolymerization of an Alexa-488 actin filament in the presence of 1 μM Cof1 and 83 nM Cy5-Srv2ΔCARP, recorded at high time resolution (0.065 s per frame) (a segment of the recording in Supplementary Movie 2). Kymographs show Alexa-488 actin (top), Cy5-Srv2ΔCARP (middle), and merge (bottom). Green bars denote episodes in which a Cy5-Srv2ΔCARP molecule was present at the pointed end of the filament. c Time records of Cy5-Srv2ΔCARP fluorescence intensity at the depolymerizing pointed ends of two actin filaments in 1 μM Cof1 and 83 nM (left; same record as in b) and 8.3 nM (right) Cy5-Srv2ΔCARP. Intensity is integrated over a 5 × 5 pixel square and smoothed with a 0.71 s sliding window. d Distribution of residence times of Cy5-Srv2ΔCARP molecules at pointed ends (n = 126; data pooled from 8.3 nM (two filaments) and 83 nM (five filaments) Cy5-Srv2ΔCARP conditions). e Length records of two filaments depolymerizing in the presence of 1 μM Cof1 and either 83 nM (black) or 8.3 nM (red) Cy5-Srv2ΔCARP. Arrowheads indicate episodes of rapid depolymerization in the red record. f, g Excerpts of length records like that in (e), red, showing measured filament length during individual Srv2 binding events (shaded intervals). Examples are shown of binding events that are (f) or are not (g) accompanied by rapid depolymerization. h Distributions of depolymerization rates of actin filaments during periods when Cy5-Srv2ΔCARP is absent (top) or present (bottom) at the pointed end of an actin filament. Source data are provided as a Source Data file.