[Relation between the structural, metabolic and "adhesive" properties of nuclear and cytoplasmic non-ribosomal RNA]

Nuclear RNAs release from nucleoproteins of isolated nuclei absorbed on a celite column in a wide range of dissociating conditions (from 1 M LiCl--2 M urea at 2 degrees C to 4 M LiCl--8 M urea at 70-80 degrees C) was demonstrated. Such a high "adhesive" heterogeneity of nuclear RNAs (i.e., variations in the tightness of RNA-protein bonds) appears to be due to the association of nuclear matrix proteins. A direct correlation was found to exist between the metabolic turnover of RNA and the tightness of its association with the nuclear matrix. Actually, the pulse label which rapidly incorporates into the RNAt greater than 50 degrees, the RNA fraction being most tenaciously bound to the matrix, could be chased later into RNAs weakly bound to it. As the RNA-matrix binding weakens, the metabolic and structural properties of a given RNA change, e.g., sedimentation coefficients decrease, while the poly(A)+-RNA content and stability increase. The "adhesive" heterogeneity was found to be inherent in not only nuclear RNAs but also in cytoplasmic non-ribosomal RNAs, showing the same correlation, i.e., the tighter the RNA--protein complex, the higher the rate of RNA turnover. Cytoplasmic RNAs which differ in their adhesiveness may fulfil various intracellular functions, since polyribosomal mRNPs and informosomal mRNPs appear to be enriched in tightly and weakly bound RNA fractions, respectively. The interrelationships between nuclear and cytoplasmic RNAs are discussed.