POLYRIBOSOME FORMATION AND RNA SYNTHESIS IN EARLY POST-FERTILIZATION STAGES OF SEA URCHIN EGG

In the unfertilized egg of the sea urchin Paracentrotus lividus it is possible to detect a small number of polyribosomes active in protein synthesis. The polyribosomal population starts to increase rapidly very soon after fertilization and the polyribosomes become progressively heavier during the first cell cycle. It is suggested that as a result of the removal of the translational inefficiency of the ribosomes following fertilization the mRNA chains become more crowded with ribosomes. Very shortly after fertilization, indeed even before the first cleavage, a rapidly labeled non-ribosomal heterogeneous RNA is synthesized that becomes attached to the polyribosomes. © 1969.