Microtubules induced to polymerize with taxol in a mammalian mitotic extract organize into aster-like arrays in a centrosome-independent process that is driven by microtubule motors and structural proteins. These microtubule asters accurately reflect the noncentrosomal aspects of mitotic spindle pole formation. We show here that colonic-hepatictumor-overexpressed gene (ch-TOGp) is an abundant component of these asters. We have prepared ch-TOGp-specific antibodies and show by immunodepletion that ch-TOGp is required for microtubule aster assembly. Microtubule polymerization is severely inhibited in the absence of ch-TOGp, and silver stain analysis of the ch-TOGp immunoprecipitate indicates that it is not present in a preformed complex and is the only protein removed from the extract during immunodepletion. Furthermore, the reduction in microtubule polymerization efficiency in the absence of ch-TOGp is dependent on ATP. These results demonstrate that ch-TOGp is a major constituent of microtubule asters assembled in a mammalian mitotic extract and that it is required for robust microtubule polymerization in an ATP-dependent manner in this system even though taxol is present. These data, coupled with biochemical and genetic data derived from analysis of ch-TOGp-related proteins in other organisms, indicate that ch-TOGp is a key factor regulating microtubule dynamics during mitosis.
This work was supported by Grant GM51542 from the National Institutes of Health.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
