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Nature. 1996 Apr 4;380(6573):451-3.

Direct observation of single kinesin molecules moving along microtubules.

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Yanagida BioMotron Project, ERATO, JRDC, Senba-Higashi, Osaka, Japan.


Kinesin is a two-headed motor protein that powers organelle transport along microtubules. Many ATP molecules are hydrolysed by kinesin for each diffusional encounter with the microtubule. Here we report the development of a new assay in which the processive movement of individual fluorescently labelled kinesin molecules along a microtubule can be visualized directly; this observation is achieved by low-background total internal reflection fluorescence microscopy in the absence of attachment of the motor to a cargo (for example, an organelle or bead). The average distance travelled after a binding encounter with a microtubule is 600 nm, which reflects a approximately 1% probability of detachment per mechanical cycle. Surprisingly, processive movement could still be observed at salt concentrations as high as 0.3 M NaCl. Truncated kinesin molecules having only a single motor domain do not show detectable processive movement, which is consistent with a model in which kinesin's two force-generating heads operate by a hand-over-hand mechanism.

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