Fig. 4.
(A) Stepping trace of the WTh\Muth heterodimer. Muth and WTh were labeled with QD-585 (blue trace) and QD-655 (red trace), respectively. WTh mostly remains in the lead during a short backward run (insert 1) and a long forward run (insert 2). (B) Plot of on-axis step size (blue dots) of WTh and Muth versus interhead separation. The step size decreases linearly (red line) with increased interhead separation and is biased forward by 10.9 ± 0.8 nm for WTh and 7.1 ± 0.7 nm for Muth. Step-size histograms (bar graphs) show that dWT = 6.5 nm whereas dMut = −2.6 nm in the lead. (C) Histogram of the angles between interhead separation and stepping vectors of Muth and WTh. (D) Model for WTh\Muth processivity. ATP binding to WTh triggers its release from the microtubule and the subsequent diffusional search is biased forward by the power stroke of the WTh linker. The weakly attached Muth moves toward WTh under linker tension.