Separation of sister chromatids in mitosis requires the Drosophila pimples product, a protein degraded after the metaphase/anaphase transition.

Mutations in the Drosophila genes pimples and three rows result in a defect of sister chromatid separation during mitosis. As a consequence, cytokinesis is also defective. However, cell cycle progression including the mitotic degradation of cyclins A and B is not blocked by the failure of sister chromatid separation, and as a result, metaphase chromosomes with twice the normal number of chromosome arms still connected in the centromeric region are observed in the following mitosis, pimples encodes a novel protein that is rapidly degraded in mitosis. Our observations suggest that Pimples and Three rows act during mitosis to release the cohesion between sister centromeres.