Dual DNA/RNA Extraction

It is sometimes desirable to extract both RNA and DNA from the same sample, especially when the sample is small. This can be achieved by isolating a total nucleic acid fraction that is then divided into two portions, which are treated differentially with either Dnase I (to remove DNA and recover RNA) or with RNase A (to selectively recover the DNA); however, this wastes half of the DNA and RNA. An alternative approach is to sequentially isolate the RNA and DNA fractions from the same sample. This protocol based on one reported by Chevillard (1 ), begins by extracting RNA as in Chapter 9 , but then re-extracts the DNA from the collected organic phases. The method described is for the extraction of both DNA/RNA from tissue but can be modifed for either blood or cell lines (see Notes 1 and 2 ).