The hydrodynamic shape, conformation, and molecular model of Escherichia coli ribosomal 5 S RNA.

The structure of ribosomal 5 S RNA has been examined using several physical biochemical techniques. Hydrodynamic measurements yield a s020,omega and eta] of 5.5 x 10(-13) x and 6.9 ml/g, respectively. Other parameters calculated from these values indicate the shape of 5 S RNA is consistent with that of a prolate ellipsoid 160 A in length and 32 A wide. Sedimentation equilibrium results show that 5 S RNA exists as a monomer in the reconstitution buffer with an apparent molecular weight of 44,000. Ultraviolet absorption difference spectra show that approximately 75% of the bases in 5 S RNA are involved in base pairing, and of these base pairs 70% are G-C and 30% are A-U. These results on the overall shape and secondary structure of 5 S RNA have been incorporated with the results of other investigators as to the possible location of single-stranded and double-stranded helical regions, and a molecular model for 5 S RNA is proposed. The molecular model consists of three double helices in the shape of a prolate ellipsoid, with two of the double helical regions at one end of the molecule. The structure is consistent with the available data on the structure and function of 5 S RNA and bears similarity to the molecular model proposed by Osterberg et al. ((1976) Eur. J. Biochem. 68, 481-487) based on small angle x-ray scattering results and the secondary structure proposed by Madison ((1968) Annu. Rev. Biochem. 37, 131-148).