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Phosphorylation and activation of human cdc25‐C by cdc2‐‐cyclin B and its involvement in the self‐amplification of MPF at mitosis.
Author(s) -
Hoffmann I.,
Clarke P.R.,
Marcote M.J.,
Karsenti E.,
Draetta G.
Publication year - 1993
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1002/j.1460-2075.1993.tb05631.x
Subject(s) - biology , cyclin b , cdc25 , cyclin dependent kinase 1 , mitosis , cyclin a , cyclin a2 , microbiology and biotechnology , cyclin b1 , xenopus , phosphorylation , cyclin dependent kinase complex , cyclin , cell cycle , biochemistry , cyclin dependent kinase 2 , protein kinase a , cell , gene
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.