[Comparative study of cytoplasmic RNA-binding proteins of eukaryotic cells: content and polypeptide composition]

The specific RNA-binding activity of cytoplasmic extracts of a number of eukaryotic cells and tissues was determined by sorption of radioactive RNA on nitrocellulose filters. This activity varies within a wide range: from 0,5 up to 80 microgram of 23S-RNA per mg of extract protein. The percentage of RNA-binding proteins as measured by their adsorption on RNA-Sepharose is 0,3--60% of total protein of cytoplasmic extracts and is well-correlated with their RNA-binding activity. The variability of the RNA-binding activity of the isolated preparations of RNA-binding proteins (from 100 to 300 microgram of 23S-RNA per mg of protein) is indicative of their qualitative differences. The analysis of the polypeptide composition of RNA-binding proteins revealed that the set of the major polypeptide chains is rather simple (with few exceptions) and includes both universal components with mol. weights of about 36,000, 49,000 and 95,000 characteristic of a number of cells and tissues and tissue- and species-specific polypeptides. Upon differentiation of rabbit reticulocytes into erythrocytes the percentage of RNA-binding proteins is decreased 4-fold and one of the three main polypeptides with the mol. weight of about 95,000 disappears. After fecundation of sea urchin ovicelles the polypeptide with the mol. weight of 37,000 disappears from the preparations of RNA-binding proteins and at the morula stage two new components with the mol. weights of about 35,000 and 26,000 appear instead of it. The germination of wheat embryos results in a two-fold increase of the percentage of RNA-binding proteins without any essential changes of the set of main polypeptide chains.