Figure 2.

Y222F mutation favors straight oligomers. (A–C) Electron micrographs of oligomers coexisting with MTs. At 10 min after the onset of reaction, the EM image of WT tubulin showed dimers and oligomers coexisted with MTs (A). For the Y222F mutant, oligomers were observed at 30 s (B) but not at 10 min (C). For darkfield microscopy images of the same samples, see Fig. 1, M–P. (D–G) Statistical analyses of oligomers. Schematic representation of the measurement (D). Oligomer length and average curvature were determined by fitting a circle to the center line of the oligomer. To unambiguously determine the curvature, only those oligomers comprising at least three heterodimers were subjected to the analyses. (E) Representative images of oligomers and (F) distribution of the length and curvature for WT(GTP), WT(GDP), Y222F(GTP), and Y222F(GDP) oligomers (n = 323, 321, 337, and 300, respectively). To show ensemble of oligomers, in the representative images (E), the oligomers were imaged at oligomer densities threefold to fivefold higher than the oligomer densities the curvature was measured. The exact condition of sample preparation is indicated in the graph legend (G). (G) The normalized distributions of the curvatures. For WT(GDP) oligomers, the grid was prepared at 5 and 30 min after the onset of reaction, but only the former is shown in E and F. The area corresponding to nearly straight oligomers with curvature <10 µm⁻¹ is highlighted in yellow in F and G.