FIGURE 4.

The kinesin-1 tail stimulates microtubule stability in a manner similar to Tau. Tubulin with or without ligand (Tail944, Tail944 A905C Mutant A+B, Tail Peptide, or hTau-40) was incubated under various microtubule-destabilizing conditions (shift to 4 °C, CaCl₂, NaCl, or dilution), and the amount of assembled microtubules (P) versus disassembled tubulin (S) was compared by gel electrophoresis in A. Representative negative stain electron micrographs of paclitaxel-stabilized microtubules (panel 1) or tubulin polymerized without paclitaxel in the presence of hTau-40 (panel 2), Tail944 A905C Mutant A+B (panel 3), or Tail944 (panels 4 and 5) are shown in B. The boxed area in panel 4 is magnified in panel 5 to show the 8-nm periodic pattern of density along the edges of the microtubule. Length, width, and periodicity values are reported as the mean ± S.D. of 100 measurements.