EVIDENCE FOR A ROLE OF CLIP-170 IN THE ESTABLISHMENT OF METAPHASE CHROMOSOME ALIGNMENT

CLIPs (cytoplasmic linker proteins) are a class of proteins believed t o mediate the initial, static interaction of organelles with microtubu les. CLIP-170, the CLIP best characterized to date, is required for in vitro binding of endocytic transport vesicles to microtubules. We rep ort here that CLIP-170 transiently associates with prometaphase chromo some kinetochores and codistributes with dynein and dynactin at kineto chores, but not polar regions, during mitosis. Like dynein and dynacti n, a fraction of the total CLIP-170 pool can be detected on kinetochor es of unattached chromosomes but not on those that have become aligned at the metaphase plate. The COOH-terminal domain of CLIP-170, when tr ansiently overexpressed, localizes to kinetochores and causes endogeno us full-length CLIP-170 to be lost from the kinetochores, resulting in a delay in prometaphase. Overexpression of the dynactin subunit, dyna mitin, strongly reduces the amount of CLIP-170 at kinetochores suggest ing that CLIP-170 targeting may involve the dynein/dynactin complex. T hus, CLIP-170 may be a linker for cargo in mitosis as well as interpha se. However, dynein and dynactin staining at kinetochores are unaffect ed by this treatment and further overexpression studies indicate that neither CLIP-170 nor dynein and dynactin are required for the formatio n of kinetochore fibers. Nevertheless, these results strongly suggest that CLIP-170 contributes in some way to kinetochore function in vivo.