1. Add 15-20 u of RNase I per 1 µg of RNA. RNase I is ≥ 90% active within pH range 7.0-8.8 at salt concentration 100-200 mM. Incubation with RNase I can be performed simultaneously with the digestion of DNA by restriction endonucleases.
2. Incubate at 37 degrees C for 30 minutes.
3. Purify DNA by spin column or phenol/chloroform extraction.