The status of small nuclear RNA in the ribonucleoprotein fibrils containing heterogeneous nuclear RNA.

hnRNP are made of two classes of unit, monoparticles and heterogeneous complexes. The monoparticles are much more easily dissociated by salt than the heterogeneous complexes. We made use of this differential salt sensitivity to determine the localization of snRNA in hnRNP. 1, About 50% of the snRNA were released by NaCl under the conditions of dissociation of monoparticles, U1 RNA which was enriched in monoparticles was preferentially released. 2, When the proteins resistant to salt dissociation were digested with proteinase K, an additional small proportion of snRNA was released, in particular a species designated 5 Sa RNA. Therefore, 5 Sa RNA seems to be preferentially associated with the proteins of heterogeneous complexes. 3, 40% of the snRNA remained associated with the hnRNA in the absence of any detectable protein. U1 and U2 RNA were the major RNAs in this fraction. The same RNA pattern was obtained for phenol-extracted RNA. The results indicate that all snRNA species are associated with the proteins of monoparticles, with those of heterogeneous complexes and with hnRNA. The existence of these pools of snRNA may reflect different functional states.