We have used indirect immunofluorescence in combination with correlative EM to subdivide the mammalian kinetochore into two domains based on the localization of specific antigens. We demonstrate here that the fibrous corona on the distal face of the kinetochore plate contains tubulin (previously shown by Mitchison, T. J., and M. W. Kirschner. 1985. J. Cell Biol. 101:755-765) and the minus end-directed, ATP-dependent microtubule motor protein, dynein; whereas a 50-kD CREST antigen is located internal to these components in the kinetochore. Tubulin and dynein can be extracted from the kinetochore by 150 mM KI, leaving other, as yet uncharacterized, components of the kinetochore corona intact. Microtubules and tubulin subunits will associate with kinetochores in vitro after extraction with 150 mM KI, suggesting that other functionally significant, corona-associated molecules remain unextracted. Our results suggest that the corona region of the kinetochore contains the machinery for chromosome translocation along microtubules.

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