Securin correct separation

The separation of sister chromatids at anaphase cannot commence until separase cleaves the cohesin subunit Scc1. Separase is regulated by an inhibitor, securin, that seems to have contradictory characteristics—it prevents Scc1 cleavage by separase, yet at the same time it is required for separase function and correct chromatid separation. Now, Nadine Hornig, Frank Uhlmann (London Research Institute, London), and colleagues explain how securin primes separase for a rapid burst of activity in mitosis.

To promote correct separase function, securin first ensures the nuclear localization of separase. Securin levels normally drop during anaphase and do not increase again until S phase. When the group expressed securin in G1, they found it increased the amount of separase found in the nucleus. But just bringing separase to the nucleus was not enough; securin also acted as a chaperone for...