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Halving of the chromosome number during meiosis I depends on the segregation of maternal and paternal centromeres. This process relies on the attachment of sister centromeres to microtubules emanating from the same spindle pole. We describe here the identification of a protein complex, Csm1/Lrs4, that is essential for monoorientation of sister kinetochores in Saccharomyces cerevisiae. Both proteins are present in vegetative cells, where they reside in the nucleolus. Only shortly before meiosis I do they leave the nucleolus and form a "monopolin" complex with the meiosis-specific Mam1 protein, which binds to kinetochores. Surprisingly, Csm1's homolog in Schizosaccharomyces pombe, Pcs1, is essential for accurate chromosome segregation during mitosis and meiosis II. Csm1 and Pcs1 might clamp together microtubule binding sites on the same (Pcs1) or sister (Csm1) kinetochores.


Journal article


Dev Cell

Publication Date





535 - 548


ATP-Binding Cassette Transporters, Cell Cycle Proteins, Cell Nucleolus, Centromere, Chromosomal Proteins, Non-Histone, Chromosome Segregation, DNA, Gene Expression Regulation, Fungal, Kinetochores, Macromolecular Substances, Meiosis, Molecular Sequence Data, Mutation, Nuclear Proteins, Phosphoproteins, Protein Transport, Saccharomyces cerevisiae, Saccharomyces cerevisiae Proteins, Schizosaccharomyces, Schizosaccharomyces pombe Proteins, Sequence Homology, Amino Acid, Sequence Homology, Nucleic Acid