Protein synthesis and distribution of ribosomal elements in ovarian oocytes and early developmental stages of Drosophila melanogaster

Protein synthesis has been investigated in cell-free preparations from mature ovarian oocytes, unfertilized and fertilized eggs, and early embryos of Drosophila melanogaster. Preparations from unfertilized eggs have a specific activity that is 5- to 6-fold higher than the activity of fractions from ovarian oocytes. There is an additional small increase in activity of preparations from fertilized eggs. The specific activity that is rapidly attained in the fertilized egg remains essentially constant for 2 to 2.5 h after fertilization, decreases sharply during blastoderm formation, and again increases during gastrulation. The activities of unfertilized eggs decline slightly during the first 2 h after oviposition, and then decrease more sharply. About 35 % of the ribosomes in preparations from both unfertilized and fertilized eggs sediment in the polyribosome region of sucrose density gradients, whereas no polyribosomes could be detected in preparations from ovarian oocytes. In both ovarian oocytes and fertilized eggs, less than 1 % of the ribosome populations were present as subunits. Additional ribonucleoprotein material of buoyant densities different from those of ribosomal subunits or ribosomes was found throughout the sucrose gradients. About 3.5 % of the ribosomes were found to be membrane-bound in preparations from both unfertilized and fertilized eggs.