The maintenance of intracellular processes, like organelle transport and cell division, depend on bidirectional movement along microtubules. These processes typically require kinesin and dynein motor proteins, which move with opposite directionality. Because both types of motors are often simultaneously bound to the cargo, regulatory mechanisms are required to ensure controlled directional transport. Recently, it has been shown that parameters like mechanical motor activation, ATP concentration and roadblocks on the microtubule surface differentially influence the activity of kinesin and dynein motors in distinct manners. However, how these parameters affect bidirectional transport systems has not been studied. Here, we investigate the regulatory influence of these three parameters using in vitro gliding motility assays and stochastic simulations. We find that the number of active kinesin and dynein motors determines the transport direction and velocity, but that variations in ATP concentration and roadblock density have no significant effect. Thus, factors influencing the force balance between opposite motors appear to be important, whereas the detailed stepping kinetics and bypassing capabilities of the motors only have a small effect.

B CUBE Center for Molecular Bioengineering and Cluster of Excellence Physics of Life Technische Universität Dresden D 01307 Dresden Germany

Center for Biophysics Department of Physics Saarland University D 66123 Saarbrücken Germany

Institute of Biotechnology of the Czech Academy of Sciences BIOCEV CZ 25250 Prague West Czech Republic

Max Planck Institute of Molecular Cell Biology and Genetics D 01307 Dresden Germany

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