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Quantitation of nanogram amounts of nucleic acids in the presence of proteins by the ethidium bromide staining technique.

Modification of the method for determining low amounts of RNA and DNA is proposed. It consists in nucleic acid staining in solution with EtBr (1 microgram/ml) followed by photography of 10 microliters drops on a UV-transparent plate under UV illumination. Densitometric measurements of the Polaroid negatives were used to construct standard concentration curves in the range of 1-16 micrograms/ml of DNA or RNA. This permitted to determine nucleic acid in amounts as little as 10 micrograms. The measurements were not influenced by the presence of proteins such as bovine serum albumin, DNase, RNase or proteinase K, thus the method proposed may be useful in determining the nucleic acid content of very small samples or of scarce biological material.