Selective regulation of kinesin-5 function by β-tubulin carboxy-terminal tails

The tubulin code hypothesis predicts that carboxy-terminal tails of tubulins create programs for selective regulation of microtubule-binding proteins, including kinesin motors. However, the molecular mechanisms that determine selective regulation and their relevance in cells are poorly understood. In this work, we report selective regulation of budding yeast kinesin-5 motors, Cin8 and Kip1, by the {beta}-tubulin tail. Cin8, but not Kip1, requires the {beta}-tubulin tail for its recruitment to the mitotic spindle. This creates a balance of both kinesin-5 motors in the spindle, and efficient mitotic progression. We identify a negatively charged patch of acidic amino acids in the {beta}-tubulin tail that mediates the interaction with Cin8 in vivo. Using in vitro reconstitution with genetically modified yeast tubulin, we demonstrate that the charged patch in the {beta}-tubulin tail increases Cin8 plus-end directed velocity and processivity. Finally, we determine that the positively charged amino-terminal extension from the Cin8 motor domain coordinates interactions with the {beta}-tubulin tail. This work provides the first demonstration of a molecular mechanism underlying selective regulation of closely related kinesin motors by tubulin tails, and how this regulation promotes proper function of the mitotic spindle.