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Melanosomes Transported by Myosin-V in Xenopus Melanophores Perform Slow 35 nm Steps

Valeria Levi ^*, Vladimir I. Gelfand , Anna S. Serpinskaya  and Enrico Gratton ^*

^* Laboratory for Fluorescence Dynamics, Physics Department, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801; and Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611

Correspondence: Address reprint requests and inquiries to Enrico Gratton, E-mail: enrico{at}scs.uiuc.edu.

We studied the motion of pigment organelles driven by myosin-V in Xenopus melanophores using a tracking technique with precision of 2 nm. The organelle trajectories showed occasional steps with a distribution centered at 35 nm and a standard deviation of 13 nm, in agreement with the step size of myosin-V determined in vitro. In contrast, trajectories of melanosomes in cells expressing a dominant negative form of myosin-V did not show steps. The step duration was in the range 20–80 ms, slower than what it would be expected from in vitro results. We speculate that the cytoplasm high viscosity may affect significantly the melanosomes' motion.

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