Mutations in the yeast kinesin-like Cin8p are alleviated by osmotic support

Loss of function of Cin8p (a yeast kinesin-like motor protein) in the absence of either Kip1p (a motor of the same family) or Dyn1p (the dynein heavy chain) is lethal. We report that cin8 mutants are sensitive to the cell wall disrupting agents calcofluor white and SDS. Conditionally lethal double mutants containing the temperature sensitive allele cin8-3 in a background deletion of either kip1 or dyn1 grew normally at the restrictive temperature when osmolytes such as sorbitol were added to the medium. Sorbitol could not alleviate the sensitivity of cin8 mutants to calcofluor and SDS. However, it rendered cells more resistant to the microtubule depolymerizing drugs benomyl and thiabendazole (TBZ). Our findings reveal a novel interaction between mitotic motor proteins and the cell wall and suggest that the induction of signaling pathways aimed at maintaining the cell wall suppresses phenotypes of mutations in microtubule-associated motor proteins through stabilization of microtubules.