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Entry into mitosis is normally blocked in eukaryotic cells that have not completed replicative DNA synthesis; this 'S-M' checkpoint control is fundamental to the maintenance of genomic integrity. Mutants of the fission yeast Schizosaccharomyces pombe defective in the S-M checkpoint fail to arrest the cell cycle when DNA replication is inhibited and hence attempt mitosis and cell division with unreplicated chromosomes, resulting in the 'cut' phenotype. In an attempt to identify conserved molecules involved in the S-M checkpoint we have screened a regulatable murine cDNA library in S. pombe and have identified cDNAs that induce the cut phenotype in cells arrested in S phase by hydroxyurea. One such cDNA encodes a novel protein with multiple calmodulin-binding motifs that, in addition to its effects on the S-M checkpoint, perturbed mitotic spindle functions, although spindle pole duplication was apparently normal. Both aspects of the phenotype induced by this cDNA product, which we term Sha1 (for spindle and hydroxyurea checkpoint abnormal), were suppressed by simultaneous overexpression of calmodulin. Sha1 is structurally related to the product of the Drosophila gene abnormal spindle (asp). These data suggest that calmodulin-binding protein(s) are important in the co-ordination of mitotic spindle functions with mitotic entry in fission yeast, and probably also in multicellular eukaryotes.


Journal article


J Cell Sci

Publication Date



111 ( Pt 24)


3609 - 3619


3T3 Cells, Amino Acid Sequence, Animals, Calmodulin, Calmodulin-Binding Proteins, Cell Division, Cell Nucleus, Cytoplasm, DNA, Complementary, Drosophila Proteins, Gene Expression Regulation, Mice, Microtubule-Associated Proteins, Mitosis, Molecular Sequence Data, Nerve Tissue Proteins, Phenotype, S Phase, Schizosaccharomyces, Sequence Homology, Amino Acid, Spindle Apparatus, Transfection