9604135 Orr-Weaver The Drosophila MEI-S332 protein is essential for sister-chromatid cohesion in meiosis. During meiosis the sister chromatids must remain attached as the homologs segregate in meiosis I, retaining cohesion until their separation in meiosis II. The phenotype of mutations in mei-S322 predicted that the protein was required to hold the sister chromatids together at their centromeres. MEI-S322 indeed localizes onto the meiotic centromeres and persists there until the sister chromatids separate in meiosis II. The mutations in MEI_S322 reveal domains of the protein crucial in male and female meiosis, as well as regions necessary for centromere localization. Unraveling the mechanism by which MEI_S322 maintains sister-chromatid cohesion and isolating other proteins that participate in the process will provide a crucial link in understanding chromosome segregation. With the isolated protein, it is possible to determine how it localizes onto centromeres and how once localized it maintains cohesion. The domains of the protein needed for localization will be further delineated and modifications of the protein accompanying localization will be investigated. Experiments are designed to distinguish whether MEI_S322 acts on the centric heterochromatin or controls the kinetochore. Several approaches will be used to recover proteins that interact with MEI_S322 to maintain cohesion. Proper segregation also necessitates precise release of sister-chromatid cohesion and the domains needed for delocalization will be mapped and modifications of the protein associated with chromosomal dissociation will be analyzed. Genetic screens will identify genes that regulate MEI-S322. Genetic and cytological tests are designed to detect proteins with analogous functions in mitosis which may either interact or control MEI-S322. Physical association between the sister chromatids, sister-chromatid cohesion, is essential for proper segregation during cell division. Sister-chromatid cohesion enables the sister chr omatids to attach to microtubules from opposite spindle poles and thus partition away from each other. In addition, the release of sister-chromatid cohesion must also be precisely regulated. In order to understand the underlying molecular basis for this precise regulation, it is critical to define the proteins that mediate such attachments and release.
