The evaluation of standard sedimentation coefficients of sodium RNA and sodium DNA from sedimentation velocity data in concentrated NaCl and CsCl solutions

Abstract

1. 1. The sedimentation velocity of the sodium and cesium salts of MS2 RNA and T7 DNA has been investigated in NaCl and CsCl solutions which range in concentrations from about 1 M to concentrations in which the macromolecules are buoyant. Over this range the product of the sedimentation coefficient and the viscosity of the solution decreases linearly with the density of the solvent. 2. 2. It is shown that the linearity is consistent with the previously published large changes in the preferential solvation of cesium DNA in concentrated salt solution. 3. 3. A method for the determination of the band shape and buoyant density of MS2 RNA in CsCl at 40° is described. The buoyant density of this cesium RNA at 25° is 1.895 g·cm −3. 4. 4. The relative viscosity at 20° of CsCl solutions in a range of concentrations from 1 to 7 M has been measured. The minimum in the viscosity vs. density curve occurs at approx. 2.5 M. At this concentration the relative viscosity is 0.92. 5. 5. Relations for the refractive index vs. density at 25° of CsCl solutions (1.00 < ϱ < 1.37) and NaCl solutions (1.00 < ϱ < 1.19) are reported.