Figure 1.

Correlation analysis of Eg5 pause forces. (a) Schematic diagram of the optical trapping assay. The tetrameric motor immobilized on a β-casein coated glass surface is propelling a microtubule. A micrometer-sized streptavidin-coated bead brought into contact with a biotinylated, end-labeled microtubule is trapped (Materials and Methods). (b) Example traces of five different Eg5-driven microtubules producing force against the optical trap. Data are displayed after a boxcar average over a 62.5 ms window. There were a total of 14 Eg5-driven microtubules tracked for a total of 432.4940 s (the total number of data points observed at 2 kHz was 864,988). Trap stiffness was on average 0.065 ± 0.006 pN/nm for these measurements. (c) Example trace showing selected pauses. Red regions are pauses selected using criteria described in the text. For this example, trap stiffness is 0.06 pN/nm. (d) Kernel-density estimation of Eg5 force distributions. The blue line represents all data before pause selection, the red line is all data after pause selection. The number of kernels is 500, and the bandwidth is 0.15 pN. Dashed lines are at a separation of 1.41 pN. The dashed line offset found by the minimization of distance from peaks to multiples of the stall force as extracted by the first peak from the autocorrelation function in (e). (e) Autocorrelation function of the Eg5 kernel-density estimation. The first peak is identified at 1.41 pN. To see this figure in color, go online.