FIGURE 5.

Nucleotide-independent movement of dynein induced by force. A, schematic of force-induced stepping experiments. Forward force is defined as the direction in which dynein normally moves (toward the microtubule minus-end). B, example trace of nucleotide-free, force-induced stepping for AAA4 mutants in a force feedback trap with 6 pN of backward load. k = 0.062 pN/nm. C, frequency of nucleotide-independent dynein movement after applying constant forward (–3 pN) or backward load (3, 6, and 10 pN). n > 25 molecules were tested at each force for each construct. Movement was scored within a 10-s time window of pulling on a dynein-coated bead attached to the microtubule. D, velocity of force-induced dynein movement with forward (–3 pN) or backward (6 and 10 pN) load (mean ± S.D.). Velocities at 3 pN backward load were not measured due to the small fraction of moving motors. GFP, green fluorescent protein.