STRUCTURAL-CHANGES IN 16S RNA FROM ESCHERICHIA-COLI UPON UNFOLDING BYUREA

The urea-induced unfolding of 16S RNA at low ionic strength has been s tudied by dynamic light scattering, uv spectroscopy, and some hydrodyn amic methods. Three components could be resolved in the photon correla tion spectra of scattered light, using the inverse Laplace transform S IPP program [G. R. Danovich and I. N. Serdyuk (1983) in Photon Correla tion Techniques in Fluid Mechanics, vol. B38, E. O. Schulz-Dubois, Ed. , Springer, Berlin/Heidelberg, New York, p. 315]. One component is ass igned to the center-of-mass translation of the RNA, another one to a c ombination of translational and internal motion, and the last to diffu sion of urea clusters. The hydrodynamic dimensions of RNA increase str ongly upon transition from 4 to 6 M urea. We conclude that up to 2 M u rea, 16S RNA is highly elongated, and coiled above 4 M urea, with a gr eat increase of the hydrodynamic dimensions of RNA being observed upon transition from 4 to 6M urea. A scheme for RNA unfolding is proposed. (C) 1993 John Wiley & Sons, Inc.