Figure 5.
KKT4 tracks with dynamic microtubule tips. (A) Selected frames (left) and kymograph (right) from Video 1 showing wild-type KKT4 (green) tracking with the disassembling tip of a microtubule (magenta). Elapsed times are in minutes:seconds. Individual KKT4 particles can also be seen diffusing on the microtubule lattice. (B) Selected frames from Video 2 showing a wild-type KKT4115–343–coated bead diffusing on the microtubule lattice and then tracking with a disassembling tip. Arrows indicate the coverslip-anchored portion of the microtubule seed. Arrowheads indicate the microtubule tip. Elapsed times are in minutes:seconds. (C) Records of bead position versus time during continuous application of tensile force. Increasing position represents assembly-coupled movement in the direction of applied force, away from the coverslip-anchored seed (e.g., red trace, <400 s). Decreasing position represents disassembly-driven motion against the applied force (e.g., red trace, >400 s). Arrows indicate “catastrophe” events when the microtubule tip switched spontaneously from assembly into disassembly. For clarity, the records are offset vertically by an arbitrary amount. Inset: Schematic of laser trap assay. Statistical data for all recorded events are provided in Table S1.