Model of actin filament branches mediated by Acanthamoeba Arp2/3 complex. The backbone of the molecular model of filamentous actin, fitted to the 2D reconstruction, is shown in pink. The first two subunits of the daughter filament, shown in red and green backbone presentation, are assigned to be Arps. The other five subunits of the complex are assigned to the rest of the projection density using the proximity information from crosslinking, genetic and yeast two hybrid experiments. The size of the regions was chosen to approximate the respective molecular weights assuming a thickness of about 5 nm. (Kurt Amann)