The Effect of Urea on the Structure of Nuclear Ribonucleoprotein Particles from Rat Liver

Abstract

Ribonucleoprotein particles were isolated in the presence of cytosolic RNase inhibitor from rat liver nuclei and exposed to increasing concentrations of urea. The average sedimentation coefficient of 90 S in a sucrose gradient decreased slightly with urea concentrations of up to 2 M. At 5 M urea the particles sedimented at about 20 S. The protein-to-RNA ratio decreased from 4 to 1.4 after treatment with 5 M urea. The proteins which are preferentially detached from the ribonucleoprotein complex are in the molecular weight range of 30000-45000. In addition, small nuclear RNAs (snRNA) were dissociated from the ribonucleoprotein particles by high urea concentrations (> 2 M). From the fact that snRNAs are dissociated from the ribonucleoprotein complex by high urea concentrations and not dissociated by high NaCl concentrations even after extensive proteolytic digestion, it is concluded that hydrogen bonds are involved in their binding to heterogeneous nuclear RNA (hnRNA).The change in the RNA conformation after addition of increasing concentrations of urea was studied by circular dichroism measurements of ribonucleoprotein particles and protein-free particle RNA. In the presence of 5 M urea the molar ellipticities at 264 nm decreased from 15

The Size and Distribution of Cytochrome c Oxidase Subunit IV mRNA between Free and Membrane‐Bound Polyribosomes

“…For the preparation of intact loosely and tightly membrane-bound polysomes in high yields, it is essential that rat liver RNase inhibitor [21], at a concentration of about 100 units/ml, is present. The free, loosely and tightly membrane-bound fractions of polysomes were phenol extracted [I61 and chromatographed on oligo(dT)-cellulose [22].…”