A study of the dielectric properties of E. coli ribosomal RNA and proteins in solution.

The permittivity of ribosomal proteins and ribosomal RNA (rRNA) in solution was measured in the range 100 kHz to 1 GHz at four different temperatures (5, 15, 25 and 35 degrees C). The experimental dielectric relaxation was analysed by the Cole-Cole equation and, from the best-fit parameters, the average values of the dipole moment and molecular radius of the proteins were obtained. The activation enthalpy was calculated from an Arrhenius plot of the relaxation time. The energy involved in the dielectric polarization of free proteins has a magnitude of about one hydrogen bond. The data on RNA were analysed according to the Mandel model. This analysis allowed the calculation of the "subunit b" as defined by Mandel. This parameter is dependent on the temperature and therefore the relaxation time does not follow the Arrhenius law. Our data thus show that, in solution, the rRNA structure is thermally rather unstable and highly flexible.