Metabolic studies on small molecular weight nuclear RNA components in human lymphocytes

Dimers of 5 S RNA and 5.8 S RNA in low molecular weight RNA preparations

When purified 5 S RNA is exposed to concentrated solutions of sodium chloride or sodium phosphate, it is partly converted to the 5' S conformer but also partly to dimers and oligomers of 5 S RNA which are stable during gel filtration and electrophoresis. Presence of 5 S dimers can not be demonstrated in cellular RNA preparations extracted with phenol. 5.8 S RNA dimers are observed in RNA from cells extracted with phenol at 40-60 degrees C. No 5.8 S dimer is observed when RNA is extracted at 0 degrees C. The amount of dimer increases with the temperature of extraction and may account for about 10% of the total 5.8 S RNA. When RNA extracted at 40-60 degrees C is electrophoresed on polyacrylamide gels under nondenaturing conditions the 5.8 S RNA dimer co-migrates with the low molecular weight RNA component L.

Small nuclear RNAs synthesis in PHA-stimulated and nonstimulated human peripheral blood lymphocytes

Five fractions of small nuclear RNAs (snRNAs) were identified in nuclei of human peripheral blood lymphocytes. They have been designated as: H, G', D, C and A (nomenclature according to Weinberg) in order to decreasing electrophoretic mobility. Their synthesis was observed from the first day of treatment with mitogen and was continued with different intensity during four days of culture. In nonstimulated lymphocytes exclusively A and G' fractions were detected but no (14C)-uridine incorporation was observed.

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.

The effect of sodium chloride on the structure of ribonucleoprotein particles from rat liver nuclei

38S (monoparticles) and greater than 50--200S ribonucleoprotein particles (polyparticles) from rat liver nuclei were treated with increasing concentrations of sodium chloride. Treatment of 38S or greater than 50--200S particles, with 0.14, 0.25, 0.5, 1.0, and 2.0M NaCl resulted in a decrease of protein to RNA ratios from 8 to 3.1 for 38S particles and from 4.0 to 1.5 for greater than 20--200S particles. Correspondingly the densities in CsCl increased. Whereas the maximum of the sedimentation profile of polyparticles decreased from 90S to 50S after treatment with increasing NaCl concentrations, a discontinuous change was found in the case of monoparticles. It was shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis that the proteins which were dissociated by NaCl were in the molecular weight range of 30--45 000. Four of the 5 small molecular weight RNAs in the range of 4.5 to 8S remained tightly associated even after treatment of polyparticles with 2.0M NaCl. When 38S or 70--200S nRNP particles were exposed to increasing concentrations of NaCl (0.25, 0.5, 1.0, 2.0M), the molar ellipticity at 264 nm increased progressively to about 40%. Upon NaCl treatment of polyparticles and successive removal of the dissociated proteins by centrifugation the increase in the positive CD band at 264 nm was only 15%.

Biosynthesis of low molecular weight RNA in mouse myeloma cells

The low molecular weight RNAs in the nucleus and cytoplasm of mouse myeloma cells have been characterized. There are major nuclear species (other than 5-S and tRNA), four of which contain 'capped' 5' termini. There are three major small cytoplasmic RNAs none of which contain 'caps'. The biosynthesis of the nuclear species when studied using [3H]adenosine as an RNA precursor is characterized by a rapid, transient appearance in the cytoplasm, followed by fixation in the nucleus. Within 15 min, the amount in the cytoplasm has reached a steady-state level maintained for 60 min, while the accumulation in nuclei is linear after a short lag (less than 5 min). When biosynthesis is studied using [Me-3H]methionine as a precursor, much less labeled RNA is present in the cytoplasm, suggesting that methylation may immediately precede fixation into the nucleus.