A direct interaction between cytoplasmic dynein and kinesin I may coordinate motor activity.

Cytoplasmic dynein and kinesin I are both unidirectional intracellular motors. Dynein moves cargo toward the cell center, and kinesin moves cargo toward the cell periphery. There is growing evidence that bi-directional motility is regulated in the cell, potentially through direct interactions between oppositely oriented motors. We have identified a direct interaction between cytoplasmic dynein and kinesin I. Using the yeast two-hybrid assay and affinity chromatography, we demonstrate that the intermediate chain of dynein binds to kinesin light chains 1 and 2. The interaction is both direct and specific. Co-immunoprecipitation experiments demonstrate an interaction between endogenous proteins in rat brain cytosol. Double-label immunocytochemistry reveals a partial co-localization of vesicle-associated motor proteins. Together these observations suggest that soluble motors can interact, potentially allowing kinesin I to actively localize dynein to cellular sites of function. There is also a vesicle population with both dynein and kinesin I bound that may be capable of bi-directional motility along cellular microtubules.