Figure 1.

Ground experiment using the space flight module and hardware. Samples contained 10 mg⋅ml⁻¹ of phosphocellullose purified tubulin and 2 mM GTP in buffer (10). Cells of 1-mm optical pathlength, at 7°C, were placed in the low gravity compartment. (Left) Upright. (Center). Flat. (Right) The cell was flat in the 1 × g centrifuge compartment. Microtubules were formed by rapidly warming the solution to 36°C. The centrifuge was on for the first 13 min only, this being the low gravity period of the subsequent space flight. Different macroscopic morphologies form depending on whether the sample container is horizontal, vertical, or spinning, at a critical moment 6 min after instigating microtubule assembly. Once formed after about 6 h, the structures are stationary and independent of the gravity direction. Samples were photographed through linear cross polarizers with a wavelength retardation plate. The blue interference color arises from microtubules oriented at about 45° and the yellow color from those at 135° (10–15).