It is not often that one gets the opportunity to solve a basic problem and discover a regulatory principle in the process. But this is precisely what is reported by Amon and co-workers on page 818 of this issue, and by Shuo et al. in Cell. They were investigating how the cell regulates exit from mitosis — the final, chromosome-segregation phase of the cell cycle — and re-entry into the first phase, G1. And they have found that the key is sequestration of a protein phosphatase called Cdc14 in the nucleolus.
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