Fig. 3.
Force and response to applied load of kinesin and dynein using motor-coated beads in an optical trap. (A) Stall in an optical trap for dyneins and DdUnc104 kinesin. TSTALL (thick double-headed arrows) is time spent above half-maximal load before detachment of motor(s). TSTALL increases with increasing dynein number and approaches the large value for a single tenacious kinesin (also see Table S1). (B) Histogram of stall force for dynein. The fit to the sum of three Gaussians (thick line) shows that the motor forces are additive. The obtained values of stall force for one, two, and three dyneins are 1.1 ± 0.3 pN, 2.0 ± 0.4 pN, and 3.1 ± 0.4 pN, respectively (Table S1). (C) Monte Carlo simulated trajectory of an endosome using experimentally determined input parameters. Four to eight weak dyneins are in a tug-of-war against one to two kinesins (see main text). Efficient minus transport with occasional reversals is seen. (Inset) Magnified view of a plus → minus reversal shows the zero-velocity TOW segment.