Dynamic localization of CLIP-170 to microtubule plus ends is coupled to microtubule assembly

CLIP-170 is a cytoplasmic Linker protein that localizes to plus ends of mic rotubules in vivo. In this study, we have characterized the microtubule-bin ding properties of CLIP-170, to understand the mechanism of its plus end ta rgeting. We show that the NH2-terminal microtubule-interacting domain of CL IP-170 alone localizes to microtubule plus ends when transfected into cells . Association of CLIP-170 with newly-formed microtubules was observed in ce lls microinjected with biotinylated tubulin, used as a tracer for growing m icrotubules. Using in vitro assays, association of CLIP-170 with recently p olymerized tubulin is also seen. Crosslinking and sedimentation velocity ex periments suggest association of CLIP-170 with nonpolymerized tubulin. We c onclude from these experiments that the microtubule end targeting of CLIP-1 70 is closely linked to tubulin polymerization.