The Kinetochore
Sister chromatids are attached to the mitotic spindle through a multiprotein complex, the kinetochore, directly assembled upon centromericDNA (constricted regions of mitotic chromosomes) Eukaryotic monocentriccentromeres are highly variable in size and sequence, so conservation between species or even different chromosomes of the same species (as occurs in Drosophila
M.) is not clear, challenging the classic view of a genetic locus. In opposition to human and Drosophila large regional centromeres,built on tandem repeats of highly repetitive DNA (satellites) elements; budding yeast contains point centromeres, built upon DNA of a defined sequence.Therefore, point mutations in budding yeast centromeres can actually abolish its activity,unlike what happens in other organisms.Despite this, some common features including
the overall organization of the repeats and well-defined epigenetic marks seem to outline a universal centromere architecture.The kinetochores persistently assemble over DNA organized around centromeric nucleosomes that contain specialized histone H3-like proteins, referred to as CENP-A (Cse4 in budding yeast and CID in Drosophila). CENP-A is essential for the recruitment of even the most distal kinetochore components examined. However the exact mechanisms by which CENP-A is loaded onto newly duplicated genome during S phase, the role of DNA sequences surrounding CENP-A-containing nucleosomes or even the regulatory mechanisms controlling assembly/disassembly of the kinetochore upon centromeres are currently not completely understood
The Kinetochore
Sister chromatids are attached to the mitotic spindle through a multiprotein complex, the kinetochore, directly assembled upon centromericDNA (constricted regions of mitotic chromosomes) Eukaryotic monocentriccentromeres are highly variable in size and sequence, so conservation between species or even different chromosomes of the same species (as occurs in Drosophila
M.) is not clear, challenging the classic view of a genetic locus. In opposition to human and Drosophila large regional centromeres,built on tandem repeats of highly repetitive DNA (satellites) elements; budding yeast contains point centromeres, built upon DNA of a defined sequence.Therefore, point mutations in budding yeast centromeres can actually abolish its activity,unlike what happens in other organisms.Despite this, some common features including
the overall organization of the repeats and well-defined epigenetic marks seem to outline a universal centromere architecture.The kinetochores persistently assemble over DNA organized around centromeric nucleosomes that contain specialized histone H3-like proteins, referred to as CENP-A (Cse4 in budding yeast and CID in Drosophila). CENP-A is essential for the recruitment of even the most distal kinetochore components examined. However the exact mechanisms by which CENP-A is loaded onto newly duplicated genome during S phase, the role of DNA sequences surrounding CENP-A-containing nucleosomes or even the regulatory mechanisms controlling assembly/disassembly of the kinetochore upon centromeres are currently not completely understood
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