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. 1993 Jan;12(1):53-63.
doi: 10.1002/j.1460-2075.1993.tb05631.x.

Phosphorylation and activation of human cdc25-C by cdc2--cyclin B and its involvement in the self-amplification of MPF at mitosis

I Hoffmann  1 , P R Clarke, M J Marcote, E Karsenti, G Draetta
Affiliations

Phosphorylation and activation of human cdc25-C by cdc2--cyclin B and its involvement in the self-amplification of MPF at mitosis

I Hoffmann et al. EMBO J. 1993 Jan.

Abstract

We have investigated the mechanisms responsible for the sudden activation of the cdc2-cyclin B protein kinase before mitosis. It has been found previously that cdc25 is the tyrosine phosphatase responsible for dephosphorylating and activating cdc2-cyclin B. In Xenopus eggs and early embryos a cdc25 homologue undergoes periodic phosphorylation and activation. Here we show that the catalytic activity of human cdc25-C phosphatase is also activated directly by phosphorylation in mitotic cells. Phosphorylation of cdc25-C in mitotic HeLa extracts or by cdc2-cyclin B increases its catalytic activity. cdc25-C is not a substrate of the cyclin A-associated kinases. cdc25-C is able to activate cdc2-cyclin B1 in Xenopus egg extracts and to induce Xenopus oocyte maturation, but only after stable thiophosphorylation. This demonstrates that phosphorylation of cdc25-C is required for the activation of cdc2-cyclin B and entry into M-phase. Together, these studies offer a plausible explanation for the rapid activation of cdc2-cyclin B at the onset of mitosis and the self-amplification of MPF observed in vivo.

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