Molecular interactions between ribosomal proteins — An analysis of S7-S9, S7-S19, S9-S19 and S7-S9-S19 interactions

Ribosomal proteins S7, S9 and S 19 fromEscherichia coli have been studied by the sedimentation equilibrium technique for possible intermolecular interaction between pairs of proteins as well as in a mixture of 3 proteins. The proteins were isolated to a purity greater than 95% and were characterized in the reconstitution buffer. It was observed that none of the proteins has a tendency to self-associate in the concentration range studied in the temperature range 3–6°C. Protein S9 behaves differently in the presence of other proteins. Analysis of the sedimentation equilibrium data for S7-S9, S9-S19 and S7-S9-S19 complexes revealed the need for considering the presence of a component of higher molecular weight in the system along with the monomers and their complexes to provide a meaningful curve-fitting of the data. Proteins S7 and S19 were found to interact with an equilibrium constant of association of 3 ± 2 × 10⁴ M⁻¹ at 3°C with a Gibbs free energy of interaction ΔG° of −5·7 kcal/mol. These data are useful for the consideration of the stabilization of the 3 0S subunit through protein-protein interactions and also help in building a topographical model of the proteins of the small subunit from an energetics point of view. Part of this work was carried out at the Marrs McLean Department of Biochemistry, Baylor College of Medicine, Houston, Texas 77030, USA.     

Nucleotide sequences of wheat-embryo cytosol 5-S and 5.8-S ribosomal ribonucleic acids

The nucleotide sequences of wheat embryo 5.8-S and 5-S rRNAs have been determined with the use of several techniques, including classic analysis of oligonucleotides generated by ribonuclease T1 and resolution on gels of terminally labelled RNA partially degraded with ribonucleases or with chemical reagents. The sequence of wheat embryo 5.8-S rRNA was found to be (formula: see text). This sequence is compared to 5-S rRNA sequences previously published for wheat and several other angiosperms.     

Characterization of 20-S and 40-S non-polysomal cytoplasmic messenger ribonucleoprotein particles from rat liver

Two populations of free messenger ribonucleoprotein (mRNP) particles, sedimenting at 20 S and 40 S respectively, were isolated from a rat liver postpolysomal supernatant. After treatment with 0.5 M KCl and recentrifugation through a sucrose layer, the mRNP particles were characterized with respect to their low-molecular-weight RNA and protein components. 40-S and 20-S particles show very different RNA patterns. Four distinct low-molecular-weight RNA species of approximately 105, 139, 187 and 256 nucleotides were found as components of the 40-S mRNPs. The 20-S mRNP particles contain one major low-Mr RNA species of approximately 243 nucleotides and a characteristic pattern of low-Mr RNAs similar to the one found in nuclear ribonucleoprotein particles. In contrast to the low-Mr RNAs found in nuclear RNP particles most of the low-Mr RNA species present in 20-S and 40-S mRNP particles are rapidly labeled after [3H]orotate administration. Whereas the low-Mr RNA composition of 20-S and 40-S mRNP particles is very different, the protein patterns of both mRNP complexes are very similar. Six major polypeptides with the following molecular weights of 117000, 79800, 76700, 53800, 43900, 36300 and several minor ones were found in both 20-S and 40-S mRNPs. In a cell-free system from wheat germs neither 20-S nor 40-S mRNP particles stimulated the incorporation of [3H]leucine into proteins. However, phenol-extracted RNA from 20-S and 40-S mRNPs stimulated total protein synthesis 16-fold and 3-fold, respectively. Furthermore, the RNA from both mRNP pools directed the synthesis of albumin in vitro.     

Reconstitution of active 30-S ribosomal subunits in vitro using heat-denatured 16-S rRNA.

30-S ribosomal subunits which have been reconstituted using heat-denatured 16-S rRNA can participate in the synthesis of lysosyme in vitro. Therefore all the information contributed by 16-S rRNA to the reconstitution process is carried in the primary sequence of this RNA. The specific protein-synthesizing activity of 30-S subunits reconstituted from 30-S subunit proteins and heat-denatured 16-S rRNA is about one third of that observed if unheated 16-S rRNA is used and is comparable to the activity of 30-S particles isolated after dissociation of 70-S ribosomes in the presence of 0.1 mM Mg2+.