Long range tRNA–tRNA electrostatic interactions in salt‐free and low‐salt tRNA solutions

An ordering of salt‐free and low‐salt tRNA solutions due to long‐range electrostatic tRNA–tRNA interactions has been studied by means of intensity and linewidth measurements of scattered light as well as small‐angle x‐ray scattering. From the position of the Bragg peak in small‐angle x‐ray scattering data an apparent intermacromolecular distance in the ordered tRNA clusters was calculated, while the angular asymmetry and photon correlation measurements of scattered light supply us with estimates of the tRNA cluster size. Based on an isolated hard sphere approximation, static and hydrodynamic radii of the tRNA clusters were always different, pointing to a more complicated pattern of macromolecular dynamics in the presence of long‐range electrostatic interactions. The order, as well as the tRNA cluster size, decreases with decreasing tRNA concentration and/or increasing counterion concentration in solution. In tRNA solutions of NaCl concentration lower than 0.1 M the electrostatic tRNA–tRNA interactions are substantial and have to be taken into account in conformational studies of the macromolecule.