Sister-chromatid cohesion via MEI-S332 and kinetochore assembly are separable functions of the Drosophila centromere

Attachment, or cohesion, between sister chromatids is essential for their p roper segregation in mitosis and meiosis [1,2]. Sister chromatids are tight ly apposed at their centromeric regions, but it is not known whether this i s due to cohesion at the functional centromere or at flanking centric heter ochromatin. The Drosophila MEI-S332 protein maintains sister-chromatid cohe sion at the centromeric region [3]. By analyzing MEI-S332's localization re quirements at the centromere on a set of minichromosome derivatives [4], we tested the role of heterochromatin and the relationship between cohesion a nd kinetochore formation in a complex centromere of a higher eukaryote. The frequency of MEI-S332 localization is decreased on minichromosomes with co mpromised inheritance, despite the consistent presence of two kinetochore p roteins. Furthermore, MEI-S332 localization is not coincident with kinetoch ore outer-plate proteins, suggesting that it is located near the DNA. We co nclude that MEI-S332 localization is driven by the functional centromeric c hromatin, and binding of MEI-S332 is regulated independently of kinetochore formation. These results suggest that in higher eukaryotes cohesion is con trolled by the functional centromere, and that, in contrast to yeast [5], t he requirements for cohesion are separable from those for kinetochore assem bly.