Before revision:  The model is motivated by {\em  experiments URLanelle motility along a microtubule (MT),  where particles are propelled by molecular motors (dynein and kinesin) along the thirteen protofilaments of the MT . In the model, particles can switch directions of motion due to "tug-of-war" events between counteracting motors.
After revision:  The model is motivated by {\em in vivo experiments URLanelle motility along a microtubule (MT), where particles are propelled by molecular motors (dynein and kinesin) along the thirteen protofilaments of the MT . In the model, particles can switch directions of motion due to "tug-of-war" events between counteracting motors.