Electron micrographs of N558 alone and with tubulin rings formed with dolastatin-10. (A) N558 adsorbed to thin carbon films and negatively stained with uranyl acetate. (B) N558 adsorbed to mica and rotary shadowed. (C) Sample images of N558 at higher magnification. (D) Histogram of lengths of 286 images of N558, measured once. When N558 and dolastatin-10 rings are mixed and then prepared for electron microscopy, one finds ring clusters, either stacked as seen in negative staining (E) or by high resolution shadowing (F). (G) Tubulin-dolastatin rings alone are thin (note shadow lengths) and devoid of associated material. (H) When these rings are mixed with N558 before preparation for electron microscopy, the rings appear slightly thicker (longer shadows) and are associated with material that commonly clusters in the center of the ring.