Small-angle X-ray titration of the complex formed between the ribosomal protein S4 and its 16S binding site, S4-RNA: a central core in the 30S subunit

Shape and compactness of the isolated ribosomal 16 S RNA and its complexes with ribosomal proteins

X-ray scattering, neutron scattering and velocity sedimentation techniques were used for studies of ribosomal 16 S RNA in the isolated state and in different complexes with ribosomal proteins. The neutron scattering curve of the ribosomal 30 S subparticle in 42% 2H2O where the protein component is contrast-matched, was taken as a standard of comparison characterizing the dimensions and shape of the 16 S RNA in situ. The following deductions result from the comparisons. The shape of the isolated 16 S RNA at a sufficient Mg2+ concentration (e.g., in the reconstruction buffer) is similar to that of the 16 S RNA in situ, i.e. in the 30 S particle, but it is somewhat less compact. The 16 S RNA in the complex with protein S4 has a shape and compactness similar to those of the isolated 16 S RNA. The 16 S RNA in the complex with four core proteins, namely S4, S7, S8 and S15, has a shape and compactness similar to those of the isolated 16 S RNA. The six ribosomal proteins S4, S7, S8, S15, S16 and S17 are necessary and sufficient for the 16 S RNA to acquire a compactness similar to that within the 30 S particle. The general conclusion is that the overall specific folding of the 16 S RNA is governed and maintained by its own intramolecular interactions, but the additional folding-up (about one-fourth of the linear size of the whole molecule) or the stabilization of the final compactness requires some ribosomal proteins.

The conformation of a large RNA fragment from the E.coli ribosomal 16S-RNA. An X-ray and neutron small-angle scattering study

A large 12S RNA fragment which constitutes the 5' two-thirds of 16S-RNA from the E. coli 30S subunit has been investigated by small-angle X-ray and neutron scattering. The results indicate that in reconstitution buffer the 12S-RNA fragment has a molecular weight of 270,000 +/- 20,000 and a radius of gyration of 7.1 nm. The scattering data are compatible with the RNA being folded into two major domains with the shapes of two adjacent, quite similar cylinders.