Protein synthesis in sea urchin eggs. I. Fertilization-induced changes in subcellular fractions

Ribosomal pellet and supernatant fractions separated by high speed centrifugation from unfertilized and fertilized sea urchin eggs have been recombined with each other and with total homogenate and tested for their capacity to incorporate valine-¹⁴C into protein. The ribosomal pellet from the fertilized egg was always active when tested with either unfertilized or fertilized egg supernatant or with unfertilized egg total homogenate. On the other hand, the unfertilized egg ribosomal fraction was always inactive. The unfertilized egg supernatant was less efficient than the supernatant derived from fertilized eggs when tested with fertilized egg ribosomal pellets. This relative lower efficiency could be attributed in part to the lower activity of amino acyl-RNA synthetase and to the unavailability of sRNA in the unfertilized egg.