Rise and fall of protein phosphorylation during meiotic maturation in oocytes of Sabellaria alveolata (polychaete annelid).

Incorporation of [32P]phosphate into proteins was monitored, in preloaded Sabellaria oocytes, during meiosis. After a fourfold increase during the transition from prophase to metaphase I, the incorporated radioactivity decreased steadily by 25% during completion of meiosis, while it slowly increased in metaphase I-blocked oocytes. Measurements of the amount and specific activity of nucleotide pools showed no variation, while total alkali-labile protein-bound phosphate was found to increase and then decrease during meiosis. Autoradiography of sodium dodecyl sulfate slabgels showed that some proteins have peculiar phosphorylation-dephosphorylation kinetics. The changes in the level of phosphorylation of proteins may be related to similar changes in maturation-promoting factor (MPF) activity.