Directional instability of microtubule transport in the presence of kinesin and dynein, two opposite polarity motor proteins

Abstract. Kinesin and dynein are motor proteins that move in opposite directions along microtubules. In this study, we examine the consequences of having kinesin and dynein (ciliary outer arm or cytoplasmic) bound to glass surfaces interacting with the same microtubule in vitro. Although one might expect a balance of op-posing forces to produce little or no net movement, we find instead that microtubules move unidirectionally for several microns (corresponding to hundreds of ATPase cycles by a motor) but continually switch be-tween kinesin-directed and dynein-directed transport. The velocities in the plus-end (0.2-0.3 #m/s) and minus-end (3.5-4 #m/s) directions were approximately half those produced by kinesin (0.5 #m/s) and ciliary dynein (6.7 #m/s) alone, indicating that the motors not con