FIGURE 4.

The transition to rectangular bundles is reversible. (A) Small angle synchrotron x-ray diffraction scans of MTs with 1% (wt/wt) 20 k PEO show bundles with rectangular symmetry. If these MTs are spun into a pellet, the supernatant is removed and the MTs are resuspended in solution with 0.2% 20 k PEO, the solution reconverts to a nematic of undistorted, undamaged MT (A), as seen by the SAXRD scan showing form factor scattering and (A, inset, scale bar = 50 nm) confirmed by whole mount electron microscopy. (B) Small angle rotating anode x-ray scans of MTs, with lower resolution and greater noise, demonstrate that MTs that were buckled 1% 20 k PEG and 150 mM NaCl, unbuckle with the addition of 2% GA. Plastic embedded electron microscopy cross sections confirm that previously buckled MTs reconvert to undistorted, unbundled MTs (B, inset, scale bar = 50 nm).