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Improved Alcohol Precipitation of DNA
This method was suggested in a BRL "Focus" article several years ago (Zeugin & Hartley, 1985). It is a useful way to avoid coprecipitation of proteins and accumulation of salt in the final dried preparation.
1. Crude preparations: Add 0.5 volumes of 7.5 M NH4OAc.
Pure preparations: Add 0.1 volumes of the same.
2. Add an amount of 95% ethanol equal to 2.5 times the new volume.
3. Continue per your favorite protocol.
Note that a subsequent BRL article (-, 1982) pointed out that precipitation in the cold is unnecessary. The process is an irreversible one, and takes place at room temperature, albeit somewhat more slowly. The same article shows that incubation at -70¡ actually inhibits complete precipitation.
-, "DNA Precipitation in the Presence of Ammonium Acetate", Focus 4(3), 12, 1982.
J.A. Zeugin & J.L. Hartley, "Ethanol Precipitation of DNA", Focus 7(4), 1-2, 1985.