Myosin V Spatially Regulates Microtubule Dynamics and Promotes the Ubiquitin-dependent Degradation of the Fission Yeast CLIP-170 Homologue, Tip1

Coordination between microtubule and actin cytoskeletons plays a crucial role during the establishment of cell polarity. In fission yeast, the microtubule cytoskeleton regulates the distribution of actin assembly at the new growing end during the monopolar-to-bipolar growth transition. Here, we describe a novel mechanism in which a myosin V modulates the spatial coordination of proteolysis and microtubule dynamics. In cells lacking a functional copy of the class V myosin, Myo52, the plus ends of microtubules fail to undergo catastrophe on contacting the cell end and continue to grow, curling around the end of the cell. We show that this actin-associated motor regulates the efficient ubiquitin-dependent proteolysis of the Schizosaccharomyces pombe CLIP-170 homologue, Tip1. Myo52 facilitates microtubule catastrophe by enhancing Tip1 removal from the plus end of growing microtubules at the cell tips. There, Myo52 and the ubiquitin receptor, Dph1, work in concert to target Tip1 for degradation.