Sequential dephosphorylation of p34(cdc2) on Thr-14 and Tyr-15 at the prophase/metaphase transition.
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.
Centre National de la Recherche Scientifique, Station Biologique, BP 74, 29682 Roscoff cedex, France. borgne@sb-roscoff.fr
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D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies; D016203:CDC2 Protein Kinase / Q000737:chemistry / Q000378:metabolism*; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000378:metabolism*; D003001:Cloning, Molecular; D005260:Female; D007700:Kinetics; D008677:Metaphase; D008969:Molecular Sequence Data; D009865:Oocytes / Q000166:cytology / Q000502:physiology; D010446:Peptide Fragments / Q000737:chemistry / Q000276:immunology; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010769:Phosphothreonine / Q000378:metabolism*; D019000:Phosphotyrosine / Q000378:metabolism*; D011418:Prophase; D054648:Protein Phosphatase 2; D011993:Recombinant Fusion Proteins / Q000302:isolation & purification; D011994:Recombinant Proteins / Q000378:metabolism; D013215:Starfish; D013379:Substrate Specificity; D020687:cdc25 Phosphatases
D000906:Antibodies; D018797:Cell Cycle Proteins; D010446:Peptide Fragments; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D010769:Phosphothreonine; D019000:Phosphotyrosine; D016203:CDC2 Protein Kinase; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D020687:cdc25 Phosphatases