Meiotic maturation of amphibian oocytes increases dephosphorylation of microinjected histones.
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Histone H2b phosphorylated by a cAMP dependent protein kinase was injected into Xenopus laevis oocytes and the hydrolysis of phosphate groups measured. Two hours after injection 60% of the (32p) histone radioactivity had been released. Direct microinjection of (32P) histone into oocyte nuclei showed that this organelle also has phosphatase activity. (3H)methylhistone and (125l)histone are not degraded for at least 4 hours in the oocyte. Exposure of oocytes to progesterone for 6 hours to induce meiotic maturation results in a threefold increase in the rate of dephosphorylation. Papaverine and cycloheximide which block maturation prevent this increment in histone phosphatase activity.
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