CENP-C is necessary but not sufficient to induce formation of functional centromere

CENP-C is an evolutionarily conserved centromeric protein. We have used the chicken DT40 cell line to test the idea that CENP-C is sufficient as well as necessary for the formation of a functional centromere, We have compared the effects of disrupting the localization of CENP-C with those of inducib ly overexpressing the protein. Removing CENP-C from the centromere causes d isassembly of the centromere protein complex and blocks cells at the metaph ase-anaphase junction. Overexpressed CENP-C is associated with an increase in errors of chromosome segregation and inhibits the completion of mitosis, However, the excess CENP-C does not disrupt the native centromeres detecta bly and does not associate with another conserved centromere protein, ZW10. The distribution of the excess CENP-C changes during the cell cycle. In me taphase, the excess CENP-C coats the chromosome arms, At the metaphase-anap hase transition, the excess CENP-C clusters, and during interphase it is pr esent in large bodies which form around pre-existing centromeres which are also clustered. These results indicate that CENP-C is necessary but not suf ficient for the formation of a functional centromere and suggest that the s tructure of CENP-C may be regulated during the cell cycle.