Differential and coordinate regulation of the eukaryotic small molecular weight RNAs

We have detected within the adult rat cerebral cortex 9 identifiable small molecular weight RNAs, K, K', L, Q, A, C, D, G', and H. These molecules are electrophoretically similar to the small RNAs found in other mammalian cells. Metabolic turnover and subcellular fractionation studies demonstrate that each of these small RNAs behave in a manner distinguishable from the other 8. In addition, 2 of the small RNAs, K and A, are under considerable developmental regulation. The results obtained suggest that no 2 of these molecules are present exclusively within the same subcellular structure. The cellular concentrations of the small RNAs were analyzed in 7 different adult rat tissues which varied 10-fold in their cellular RNA concentrations. The cellular levels of the cytoplasmic RNAs, 28 S, 18 S, and 5 S rRNA, 4 S tRNA, K, and L, were found to be a function of the total cellular RNA concentration. In contrast, the cellular levels of the nuclear RNAs, A, C, D, and H, varied slightly between tissues and were independent of the total cellular RNA concentration. However, these variations in the levels of the nuclear RNAs were significant in that they revealed these molecules are coordinately regulated.