kinetochore holds the sister chromatids together and attaches them to the spindle fibers.
what holds the sister chromatids together and attaches them to the spindle fibers?
kinetochore
kinetochore





























a kinetochore (, ) is a disc-shaped protein structure associated with duplicated chromatids in eukaryotic cells where the spindle fibers attach during cell division to pull sister chromatids apart. the kinetochore assembles on the centromere and links the chromosome to microtubule polymers from the mitotic spindle during mitosis and meiosis. its proteins also help to hold the sister chromatids together and play a role in chromosome editing. details of the specific areas of origin are unknown.
kinetochore
in the transition from metaphase to anaphase, it is crucial that sister chromatids are properly and simultaneously separated to opposite ends of the cell. separation of sister-chromatids is initially strongly inhibited to prevent premature separation in late mitosis, but this inhibition is relieved through destruction of the inhibitory elements by the anaphase-promoting complex (apc) once sister-chromatid bi-orientation is achieved. one of these inhibitory elements is securin, which prevents the destruction of cohesin, the complex that holds the sister-chromatids together, by binding the protease separase which targets scc1, a subunit of the cohesin complex, for destruction. in this system, the phosphatase cdc14 can remove an inhibitory phosphate from securin, thereby facilitating the destruction of securin by the apc, releasing separase. as shown by uhlmann et al., during the attachment of chromosomes to the mitotic spindle the chromatids remain paired because cohesion between the sisters prevents separation. cohesion is established during dna replication and depends on cohesin, which is a multisubunit complex composed of scc1, scc3, smc2, and smc3. in yeast at the metaphase-to-anaphase transition, scc1 dissociates from the chromosomes and the sister chromatids separate. this action is controlled by the esp1 protein, which is tightly bound by the anaphase inhibitor pds1 that is destroyed by the anaphase-promoting complex. in order to verify that esp1 does play a role in regulating scc1 chromosome association, cell strains were arrested in g1 with an alpha factor. these cells stayed in arrest during the development. esp1-1 mutant cells were used and the experiment was repeated, and scc1 successfully bound to the chromosomes and remained associated even after the synthesis was terminated. this was crucial in showing that with esp1, scc1 is hindered in its ability to become stably associated with chromosomes during g1, and esp1 can in fact directly remove scc1 from chromosomes.
biochemical switches in the cell cycle