Denaturation of RNA with dimethyl sulfoxide

The denaturation of single‐stranded and double‐stranded RNA's in solutions with varying proportions of dimethyl sulfoxide has been followed by changes in absorbancy, optical rotation, and—with a double‐stranded form of bacteriophage of MS2 RNA— infectivity for bacterial spheroplasts. By these criteria the RNA's studied, including the synthetic polynucleotide rG:rC, are completely denatured at room temperature in high concentrations of this solvent. In lower concentrations, the Tm of the RNA preparation is decreased only slightly as the dimethyl sulfoxide concentration is raised until a critical concentration is reached. The Tm falls sharply with small further increases in dimethyl sulfoxide concentration. Sedimentation studies can be conducted directly in these media. The determination of sedimentation velocity in 99% dimethyl sulfoxide containing 0.001M EDTA provides a reliable estimate of RNA molecular weights.