Sequential dephosphorylation of p34(cdc2) on Thr-14 and Tyr-15 at the prophase/metaphase transition |
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Authors: | A Borgne L Meijer |
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Affiliation: | Centre National de la Recherche Scientifique, Station Biologique, BP 74, 29682 Roscoff cedex, France. borgne@sb-roscoff.fr |
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Abstract: | The G2-M transition of the cell cycle is triggered by the p34(cdc2)/cyclin B kinase. During the prophase/metaphase transition, the inactive, Thr-14/Tyr-15 phosphorylated form of p34(cdc2) (TP-YP) is modified to an active, Thr-14/Tyr-15 dephosphorylated form (T-Y) by the cdc25 dual-specificity phosphatase. Using highly synchronized starfish oocytes as a cellular model, we show that dephosphorylation in vivo and in vitro occurs in two steps: Thr-14 dephosphorylation precedes Tyr-15 dephosphorylation. The transient intermediate form (T-YP), which can be obtained in vitro by treatment of TP-YP by protein phosphatase 2A, displays low but significant kinase activity. These results raise the possibility that the intermediate form T-YP may be involved in the autocatalytic amplification of the p34(cdc2)/cyclin B complex through phosphorylation/activation of the cdc25 phosphatase and phosphorylation/inactivation of the wee1 kinase. |
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