text: During mitosis, each sister chromatid forming the complete chromosome has its own kinetochore. Distinct sister kinetochores can be observed at first at the end of G2 phase in cultured mammalian cells. These early kinetochores show a mature laminar structure before the nuclear envelope breaks down. The molecular pathway for kinetochore assembly in higher eukaryotes has been studied using gene knockouts in mice and in cultured chicken cells, as well as using RNA interference (RNAi) in C. elegans, Drosophila and human cells, yet no simple linear route can describe the data obtained so far.
  The first protein to be assembled on the kinetochore is CENP-A (Cse4 in Saccharomyces cerevisiae). This protein is a specialized isoform of histone H3. CENP-A is required for incorporation of the inner kinetochore proteins CENP-C, CENP-H and CENP-I/MIS6. The relation of these proteins in the CENP-A-dependent pathway is not completely defined. For instance, CENP-C localization requires CENP-H in chicken cells, but it is independent of CENP-I/MIS6 in human cells. In C. elegans and metazoa, the incorporation of many proteins in the outer kinetochore depends ultimately on CENP-A.
  Kinetochore proteins can be grouped according to their concentration at kinetochores during mitosis: some proteins remain bound throughout cell division, whereas some others change in concentration. Furthermore, they can be recycled in their binding site on kinetochores either slowly (they are rather stable) or rapidly (dynamic).
  Proteins whose levels remain stable from prophase until late anaphase include constitutive components of the inner plate and the stable components of the outer kinetocore, such as the Ndc80 complex, KNL/KBP proteins (kinetochore-null/KNL-binding protein), MIS proteins and CENP-F. Together with the constitutive components, these proteins seem to organize the nuclear core of the inner and outer structures in the kinetochore.