CLIP-170 highlights growing microtubule ends in vivo

A chimera with the green fluorescent protein (GFP) has been constructed to visualize the dynamic properties of the endosome-microtubule linker protein CLIP170 (GFP-CLIP170). GFP-CLIP170 binds in stretches along a subset of mi crotubule ends. These fluorescent stretches appear to move with the growing tips of microtubules at 0.15-0.4 mu m/s, comparable to microtubule elongat ion in vivo. Analysis of speckles along dynamic GFP-CLIP170 stretches sugge sts that CLIP170 treadmills on growing microtubule ends, rather than being continuously transported toward these ends. Drugs affecting microtubule dyn amics rapidly inhibit movement of GFP-CLIP170 dashes. We propose that GFP-C LIP170 highlights growing microtubule ends by specifically recognizing the structure of a segment of newly polymerized tubulin.