KIF1B, A NOVEL MICROTUBULE PLUS END-DIRECTED MONOMERIC MOTOR PROTEIN FOR TRANSPORT OF MITOCHONDRIA

To further elucidate the mechanism of organelle transport, we cloned a navel member of the mouse kinesin superfamily, KIF1B. This N-terminal-type motor protein is expressed ubiquitously in various kinds of tissues. In situ hybridization revealed that KIF1B is expressed abundantly in differentiated nerve cells. Interestingly, KIF1B works as a monomer, having a microtubule plus end-directed motility, Our rotary shadowing electron microscopy revealed mostly single globular structures. Immunocytochemically, KIF1B was colocalized with mitochondria in vivo. Furthermore, a subcellular fractionation study showed that KIF1B was concentrated in the mitochondrial fraction, and purified KIF1B could transport mitochondria along microtubules in vitro. These data strongly suggested that KIF1B works as a monomeric motor for anterograde transport of mitochondria.