3D protein models. 3D protein models of human alpha-skeletal actin (A) and corresponding actins from fly (B), urochordate (C), branchiostoma (D), plant (E) and yeast (F). The secondary structures at the amino terminus of the protein are indicated by dark blue shading and the secondary structures at the C-terminus are colored red. The numbers indicate the subunits of the protein. White arrows point out the main differences between the models. The sites of these differences are highlighted with corresponding coloring in Figure 1.