The Structure of the -Tubulin Small Complex: Implications of Its Architecture and Flexibility for Microtubule Nucleation

Supplemental Materials

This article contains the following supporting material:

• Figure S1 - Alignment and averaging of volumes 3,4 and 5. A) The reconstruction of particles from class 3 (Figure 1C). B) The reconstruction of particles from class 4 in its original orientation (left) and aligned to volume 3 (right). C) The reconstruction of particles from class 5 in its original (left) and aligned (right) orientations. D) The average of the three aligned structures, weighted for the size of each class.
• Figure S2 - Incompatability of γ-TuSC structure and the microtubule lattice. A) Simulated EM density of two α/β-tubulin dimers associated laterally as in the microtubule are shown in green (β) and pink (α). The center-to-center distances between tubulins are 53 Å for lateral interactions and 40 Å for longitudinal interactions. The average γ-TuSC structure, with the minimum observed inter-Tub4p distance of 70 Å, is shown to highlight the incompatibility of this distance with either longitudinal (bottom) or lateral (right) contacts with the microtubule lattice. B) Movement of the mobile arm can bring the Tub4p densities to the correct distance to make lattice-like longitudinal contacts with α/β-tubulin (bottom - the same configuration as Figure 7B). Further movement can bring the Tub4p densities close enough to make lateral contacts with α/β-tubulin, but with significant overlap (about 10%) of the density (right).