FIGURE 2:

Delphilin is a nucleator. (A) Actin assembly (2 μM) was triggered by the addition of salts and the indicated concentration of mDelFFC. After 5 min, filaments were stabilized with Alexa488-phalloidin, diluted, and adsorbed to poly-l-lysine–coated coverslips. Typical fields of view are shown for a range of concentrations, as indicated. Increasing concentrations of Delphilin resulted in increasing numbers of filaments, indicating that Delphilin nucleates. The shorter filaments induced by Delphilin suggest that pointed end growth dominates under these conditions. (B) A total of 0.25 μM Alexa488- and Alexa647-phalloidin-stabilized filaments were mixed and sheared. Immediately after shearing (t = 0) filaments were short and monochromatic. After an hour (t = 60), the filament length depended on the conditions. Reannealing is readily apparent when only buffer is added. Short filaments, indistinguishable from t = 0, are seen in the presence of 10 nM capping protein or Delphilin, demonstrating that Delphilin remains bound to filament ends for long periods of time. Scale bars = 10 μm.