Fractionation with ethanol of nucleic acids from viroid-infected plants.

A combination of high salt and low ethanol concentration allowed the fractionation of nucleic acids extracted from viroid-infected leaves. By adding 0.4-0.5 vol of ethanol to 1 vol of a solution in 2 M LiCl of nucleic acids (containing mainly DNA, 4S, 5S, 7S, and viroid RNAs), 85% of the DNA and 75% of the 4S RNA remained in solution, from where they could be recovered by increasing the ethanol concentration, whereas almost all 5S, 7S, and viroid RNAs precipitated. When this process was repeated three times a 95% elimination of the initial DNA and 4S RNA was achieved. The method can be of special interest in viroid purification considering that DNA and 4S RNA are the most abundant contaminants in the starting solution of nucleic acids. It is suggested that the highly ordered secondary structure of viroid RNA may be responsible for its particular behavior in the ethanol fractionation of nucleic acids.