Hyperphosphorylation of the N-terminal domain of Cdc25 regulates activity toward cyclin B1/Cdc2 but not cyclin A/Cdk2 - PubMed (original) (raw)

. 1997 Nov 7;272(45):28607-14.

doi: 10.1074/jbc.272.45.28607.

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Hyperphosphorylation of the N-terminal domain of Cdc25 regulates activity toward cyclin B1/Cdc2 but not cyclin A/Cdk2

B G Gabrielli et al. J Biol Chem. 1997.

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Abstract

Cdc25 regulates entry into mitosis by regulating the activation of cyclin B/cdc2. In humans, at least two cdc25 isoforms have roles in controlling the G2/M transition. Here we show, using bacterially expressed recombinant proteins, that two cdc25B splice variants, cdc25B2 and cdc25B3, are capable of activating cyclin A/cdk2 and cyclin B/cdc2, but that mitotic hyperphosphorylation of these proteins increases their activity toward only cyclin B1/cdc2. Cdc25C has only very low activity in its unphosphorylated form, and following hyperphosphorylation it will efficiently catalyze the activation of only cyclin B/cdc2. This was reflected by the in vivo activity of the immunoprecipitated cdc25B and cdc25C from interphase and mitotic HeLa cells. The increased activity of the hyperphosphorylated cdc25s toward cyclin B1/cdc2 was in large part due to increased binding of this substrate. The substrate specificity, activities, and timing of the hyperphosphorylation of cdc25B and cdc25C during G2 and M suggest that these two mitotic cdc25 isoforms are activated by different kinases and perform different functions during progression through G2 into mitosis.

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