The Polo-like kinase Plx1 is a component of the MPF amplification loop at the G2/M-phase transition of the cell cycle in Xenopus eggs.
We have investigated whether Plx1, a kinase recently shown to phosphorylate cdc25c in vitro, is required for activation of cdc25c at the G2/M-phase transition of the cell cycle in Xenopus. Using immunodepletion or the mere addition of an antibody against the C terminus of Plx1, which suppressed its activation (not its activity) at G2/M, we show that Plx1 activity is required for activation of cyclin B-cdc2 kinase in both interphase egg extracts receiving recombinant cyclin B, and cycling extracts that spontaneously oscillate between interphase and mitosis. Furthermore, a positive feedback loop allows cyclin B-cdc2 kinase to activate Plx1 at the G2/M-phase transition. In contrast, activation of cyclin A-cdc2 kinase does not require Plx1 activity, and cyclin A-cdc2 kinase fails to activate Plx1 and its consequence, cdc25c activation in cycling extracts.
Abrieu
A
A
Centre de Recherches de Biochimie Macromoléculaire, CNRSUPR 1086, 34293 Montpellier cedex 5, France.
Brassac
T
T
Galas
S
S
Fisher
D
D
Labbé
J C
JC
Dorée
M
M
D000818:Animals; D016203:CDC2 Protein Kinase / Q000378:metabolism / Q000502:physiology; D018797:Cell Cycle Proteins / Q000378:metabolism; D019925:Cyclin A / Q000378:metabolism; D019926:Cyclin B / Q000378:metabolism; D004789:Enzyme Activation; D016195:G2 Phase / Q000502:physiology*; D016200:Maturation-Promoting Factor / Q000378:metabolism*; D008540:Meiosis; D008938:Mitosis / Q000502:physiology*; D010063:Ovum / Q000166:cytology / Q000201:enzymology*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism / Q000502:physiology*; D014981:Xenopus; D029867:Xenopus Proteins; D020687:cdc25 Phosphatases; D000097869:Polo-Like Kinase 1
D016203:CDC2 Protein Kinase; D018797:Cell Cycle Proteins; D019925:Cyclin A; D019926:Cyclin B; D016200:Maturation-Promoting Factor; D017346:Protein Serine-Threonine Kinases; D029867:Xenopus Proteins; D020687:cdc25 Phosphatases; C101085:Plk1 protein, Xenopus; D000097869:Polo-Like Kinase 1