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Cell. 2007 Mar 23;128(6):1133-45.

Substrate competition as a source of ultrasensitivity in the inactivation of Wee1.

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1
Department of Chemical and Systems Biology, Stanford University School of Medicine, Center for Clinical Sciences Research, Stanford, CA 94305-5174, USA.

Abstract

The mitotic regulators Wee1 and Cdk1 can inactivate each other through inhibitory phosphorylations. This double-negative feedback loop is part of a bistable trigger that makes the transition into mitosis abrupt and decisive. To generate a bistable response, some component of a double-negative feedback loop must exhibit an ultrasensitive response to its upstream regulator. Here, we experimentally demonstrate that Wee1 exhibits a highly ultrasensitive response to Cdk1. Several mechanisms can, in principle, give rise to ultrasensitivity, including zero-order effects, multisite phosphorylation, and competition mechanisms. We found that the ultrasensitivity in the inactivation of Wee1 arises mainly through two competition mechanisms: competition between two sets of phosphorylation sites in Wee1 and between Wee1 and other high-affinity Cdk1 targets. Based on these findings, we were able to reconstitute a highly ultrasensitive Wee1 response with purified components. Competition provides a simple way of generating the equivalent of a highly cooperative allosteric response.

PMID:
17382882
DOI:
10.1016/j.cell.2007.01.039
[Indexed for MEDLINE]
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