[Synthesis of ribosomal proteins in early development of the loach]

The synthesis of ribosomal proteins (r-proteins) in the loach embryos was studied by the way of analysis of protein-labeled ribosomes isolated from the cytoplasm and purified from de novo synthesized polypeptide and contaminating proteins. The ribosomes at the mid-blastula and mid-gastrula stages were shown to contain no de novo synthesized proteins. The synthesis of r-proteins at the stage of organogenesis was revealed by sedimentation analysis of ribosomes in the gradient of sucrose concentrations, density analysis in the gradient of cesium chloride and analysis of the distribution of radioactivity in r-proteins separated from the labelled ribosomes by electrophoresis in polyacrilamide gel. At the stage of organogenesis, the exchange of ribosomal proteins with de novo synthesized r-proteins continues under the conditions of complete inhibition of RNA synthesis and incubation of unlabeled ribosomes with the labelled cytosol. The correlation between the absence of rRNA and r-protein syntheses at the early developmental stages and possible causes of the independence of r-protein synthesis and exchange from the simultaneous rRNA synthesis at the stage of organogenesis are discussed.