Stimulation of endogenous protein phosphorylation in oocytes of Sabellaria alveolata (polychaete annelid) at meiosis reinitiation induced by protease, fertilization, or ionophore A 23187

Incorporation of [32P]-phosphate into proteins was enhanced when Sabellaria oocytes were stimulated with specific protease to continue from prophase I block to metaphase I block. The rate of incorporation was increased 50 fold between onset of treatment and germinal vesicle breakdown (GVB). The same result was obtained when release from prophase block involved fertilization, or activation with ionophore A 23187. In all cases, meiosis was associated with phosphorylation of an 18,000 dalton protein, which is perhaps not labeled in prophase-blocked oocytes. Phosphorylation of a 38,000–40,000 dalton doublet of membrane proteins, which are among the main phosphorylated proteins in intact oocytes, was also strongly enhanced in vitro in homogenates prepared from oocytes following release from prophase block.