Figure 4.

Eg5 drives the sliding component of flux. (a) Small molecule inhibitors of Eg5 cause a dose-dependent inhibition of flux. The sliding component of flux was measured using cross-correlation between sequential images. (b) Variation of flux rate in control spindles. Note large spindle-to-spindle and preparation-to-preparation variation. Flux rate was approximately constant in individual spindles over a period of minutes. (c) Model showing how the plus-end-directed mitotic kinesin Eg5 may drive the sliding component of flux by pushing anti-parallel microtubules apart. Open arrows indicate the direction that Eg5 walks on microtubules, driven by ATP hydrolysis. The closed arrows indicate the resulting microtubule sliding if the Eg5 molecule is static. The springs are drawn to emphasize that the flux motors are probably working against a mechanical load that limits sliding rate. The molecular nature of this load is unknown. See Miyamoto et al. (2004) for details.