The Effect of Sodium Chloride on the Structure of Ribonucleoprotein Particles from Rat Liver Nuclei

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Abstract
Monoparticles [385] and > 50-200S ribonucleoprotein particles (polyparticles) from rat liver nuclei were treated with increasing concentrations of NaCl. Treatment of 38S or > 50-200S particles with 0.14, 0.25, 0.5, 1.0, and 2.0 M 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 > 50-200S particles. The densities in CsCl increased correspondingly. 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. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that the proteins which were dissociated by NaCl were in the MW range of 30-45,000. Four of the 5 small MW RNA in the range of 4.5-8S remained tightly associated even after treatment of polyparticles with 2.0 M NaCl. When 38S or 70-200S nRNP particles were exposed to increasing concentrations of NaCl (0.25, 0.5, 1.0, 2.0 M), 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 circular dichroism band at 264 nm was only 15%.