Effect of sodium ion concentration on transfer RNA conformation in solution studied by Rayleigh light scattering

The sodium ion concentration dependent conformational changes of transfer RNA (unfractionated tRNA from baker's yeast) have been studied in unbuffered aqueous solutions by Rayleigh light scattering. Changes of the optical parameters of the molecule indicated the following conformational changes of tRNA with increasing NaCl concentration: in salt-free solution tRNA molecules have an irregular hairpin loop-like structure in which the orientation of base rings is not correlated. Upon addition of a small amount of NaCl (0.005 M) an increasing ordering of this structure is observed. In 0.1 M-NaCl the molecule has an extended structure with ordered regions (arms). Further increase of sodium ion concentration up to 2 M results in folding of the extended structure and formation of a compact and rigid conformation in which most of the bases are nearly perpendicular to the symmetry axis of the molecule.