CONFORMATION OF RIBOSOMAL-PROTEINS FREE IN SOLUTION AND BOUND TO RIBOSOMAL-RNA

The conformation of [Escherichia coli] ribosomal proteins free in solution was studied by circular dichroism (CD) and the proteins possessed unique conformations. The ribosomal proteins which contain aromatic amino acid residues and disulfide bonds appear to have unique tertiary structures as shown by the presence of near UV CD bands. Estimations of average secondary structure based on the far-UV CD spectra suggest the presence of significant amount of .alpha. helix and .beta. structure. These unique secondary and tertiary structures are extensively disrupted by guanidinium chloride (GdmCl). Broad conformational transition profiles are observed for the denaturation of GdmCl in the concentration range of 0-3.5 M. Upon removal of the denaturant, the proteins from the 50S subunits are completely renatured, but partial renaturation of the proteins from the 30S subunits is observed. These unique conformations of ribosomal proteins are sensitive to ionic strength of the medium. The conformations of the proteins bound in the ribosomal particles in the functional medium and in reconstitution buffer were approximated from CD studies by subtracting the RNA contribution from the CD spectrum of the intact ribosome and were different from the corresponding conformations free in solution. The change of conformation when the proteins are bound to the RNA may have significant relevance to the interactions of the proteins and the RNA in the assembly of functional ribosomal particles.