ACTIVATION OF P34CDC2 KINASE BY CYCLIN IS NEGATIVELY REGULATED BY CYCLIC AMP-DEPENDENT PROTEIN-KINASE IN XENOPUS-OOCYTES

Microinjection of a bacterially expressed stable Δ90 sea urchin cyclin B into Xenopus prophase oocytes, in absence or presence of cycloheximide, provokes the activation of histone H1 kinase and the tyrosine dephosphorylation of p34cdc2 Unexpectedly, when prophase oocytes are submitted to a treatment known to elevate the intracellular cAMP level (3-isobutyl-1-methylxanthine and cholera toxin), Δ90 cyclin has no effect and the oocytes remain blocked in prophase. This inhibition is reverted by the microinjection of the inhibitor of cAMP-dependent protein kinase. When Δ90 cyclin is microinjected into oocytes depleted of endogenous cyclins (cycloheximide-treated metaphase I) and in the presence of a high intracellular concentration of cAMP, p34cdc2 kinase is tyrosine rephosphorylated. Altogether, our results indicate that in Xenopus oocyte, cAMP-dependent protein kinase (A-kinase) controls the formation of the cyclin B/p34cdc2 complex which remains inactive and tyrosine phosphorylated. © 1992.