The Caenorhabditis elegans JIP3 protein UNC-16 functions as an adaptor to link kinesin-1 with cytoplasmic dynein.

Kinesin-1 is a microtubule plus-end-directed motor that transports various cargos along the axon. Previous studies have elucidated the physical and genetic interactions between kinesin-1 and cytoplasmic dynein, a microtubule minus-end-directed motor, in neuronal cells. However, the physiological importance of kinesin-1 in the dynein-dependent retrograde transport of cargo molecules remains obscure. Here, we show that Caenorhabditis elegans kinesin-1 forms a complex with dynein via its interaction with UNC-16, which binds to the dynein light intermediate (DLI) chain. Both kinesin-1 and UNC-16 are required for localization of DLI-1 at the plus ends of nerve process microtubules. In addition, retrograde transport of APL-1 depends on kinesin-1, UNC-16, and dynein. These results suggest that kinesin-1 mediates the anterograde transport of dynein using UNC-16 as a scaffold and that dynein in turn mediates the retrograde transport of cargo molecules in vivo. Thus, UNC-16 functions as an adaptor for kinesin-1-mediated transport of dynein.