STUDIES OF THE KINETICS AND IONIC REQUIREMENTS FOR THE PHOSPHORYLATION OF RIBOSOMAL PROTEIN-S6 AFTER FERTILIZATION OF ARBACIA-PUNCTULATA EGGS

Fertilization of the eggs of the sea urchin A. punctulata is followed by the phosphorylation of ribosomal protein S6. The increase in phosphorylation starts at the same time that protein synthesis begins to increase, and leads to the appearance of mono-, di- and triphosphorylated S6 derivatives. Essentially all the S6 is phosphorylated by 1st cleavage. This phosphorylation requires the occurrence of the normal Ca2+ transient and the consequent Na+-H+ exchange. Protein synthesis can be partially activated by an increase in intracellular pH brought about by weak bases, but this neither causes S6 phosphorylation, nor the inactivation of the specific S6 phosphatase present in unfertilized Arbacia eggs.