Centromeric chromatin in fission yeast

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A fundamental requirement for life is the ability of cells to divide properly and to pass on to their daughters a full complement of genetic material. The centromere of the chromosome is essential for this process, as it provides the DNA sequences on which the kinetochore (the proteinaceous structure that links centromeric DNA to the spindle microtubules) assembles to allow segregation of the chromosomes during mitosis. It has long been recognized that kinetochore assembly is subject to epigenetic control, and deciphering how centromeres promote faithful chromosome segregation provides a fascinating intellectual challenge. This challenge is made more difficult by the scale and complexity of DNA sequences in metazoan centromeres, thus much research has focused on dissecting centromere function in the single celled eukaryotic yeasts. Interestingly, in spite of similarities in the genome size of budding and fission yeasts, they seem to have adopted some striking differences in their strategy for passing on their chromosomes. Budding yeast have "point" centromeres, where a 125 base sequence is sufficient for mitotic propagation, whereas fission yeast centromeres are more reminiscent of the large repetitive centromeres of metazoans. In addition, the centromeric heterochromatin which coats centromeric domains of fission yeast and metazoan centromeres and is critical for their function, is largely absent from budding yeast centromeres. This review focuses on the assembly and maintenance of centromeric chromatin in the fission yeast.