Initial activation of cyclin-B1-cdc2 kinase requires phosphorylation of cyclin B1.
At the G(2)/M transition of the cell cycle, the cdc25c phosphatase dephosphorylates inhibitory residues of cdc2, and cyclin-B-cdc2 kinase (MPF) is activated. Phosphorylation of cyclin B1 induces its nuclear accumulation, and, since cdc25c is also believed to accumulate and activate shortly before G(2)/M in the nucleus, it has been proposed that this induces cyclin-B1-cdc2 kinase activation. We demonstrate that cyclin B1 phosphorylation has another essential function in vivo: it is required for cdc25c and MPF activation, which does not require nuclear accumulation of cyclin B1, and occurs in the cytoplasm.
Peter
Marion
M
Centre de Recherches de Biochimie Macromoléculaire, CNRS UPR 1086, 1919 route de Mende, F-34293 Montpellier cedex 5, France.
Le Peuch
Christian
C
Labbé
Jean-Claude
JC
Meyer
April N
AN
Donoghue
Daniel J
DJ
Dorée
Marcel
M
D000818:Animals; D016203:CDC2 Protein Kinase / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000378:metabolism; D019926:Cyclin B / Q000378:metabolism*; D056744:Cyclin B1; D004789:Enzyme Activation; D016200:Maturation-Promoting Factor / Q000378:metabolism*; D009865:Oocytes; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D014981:Xenopus; D029867:Xenopus Proteins; D020687:cdc25 Phosphatases / Q000378:metabolism; D000097869:Polo-Like Kinase 1
D016203:CDC2 Protein Kinase; D018797:Cell Cycle Proteins; D019926:Cyclin B; D056744:Cyclin B1; D016200:Maturation-Promoting Factor; D017346:Protein Serine-Threonine Kinases; D029867:Xenopus Proteins; D020687:cdc25 Phosphatases; C101085:Plk1 protein, Xenopus; D000097869:Polo-Like Kinase 1