Ethanol Precipitation of DNA

''For RNA use the same protocol except 3 volumes of EtOH, and spin at 4oC. RNA has greater solubility at room temperature than DNA.''

Materials:

 * Sodium acetate (3 M pH 5.2)
 * EtOH (95-100%; chilled)
 * EtOH (70%)
 * TE (10 mM Tris-Cl pH 7.5, 1 mM EDTA)

Method:

 * 1) Add one-tenth (1/10) volume of 3 M sodium acetate to the nucleic acid solution. Mix well.  If the volume of a DNA solution is 200 µl, then add 20 µl of 3 M NaOAc (or 10 µl) and 500 µl of 95% EtOH. Slightly less 3 M NaOAc is sufficient (1/20 volume) if DNA concentrations are high>1 µg/ml. 
 * 2) Add 2.5 volumes of 95% ethanol to the DNA sample, invert several times to mix and incubate on ice or -20 C for 10 minutes.  DNA can be stored overnight in 95% EtOH.   If your DNA solution is more than 300 µL, split the volume into different microfuge tubes to accommodate the additional ethanol volume. 
 * 3) Pellet DNA in a microcentrifuge (if using 1.5 ml tubes) for 10 minutes at full speed (~12,000 rpm) at room temperature.
 * 4) Pour off the supernatant and drain on a kimwipe for 1 minute. Alternatively, pour off the supernatant, then briefly respin the tubes and pull off trace amounts of ethanol solution with a drawn out pipet. This will allow you to quicky dry the pellet and resuspend the DNA.
 * 5) If excess salt is potentially detrimental for the next steps, then wash with cold 70% ethanol (corresponding to 2 volumes of the original aqueous solution), incubate on ice 10 minutes and spin 5 minutes at top speed in a microcentrifuge decant supernatant or draw off liquid as in step 4.   If DNA concentration is low (< 20 ng/ml) or size is small (< 100 bp), then increase ice incubation time to 1 hour and spin 20-30 minutes. 
 * 6) Air dry or vacuum-dry to remove all traces of residual EtOH.
 * 7) Dissolve DNA in appropriate amount of TE.  Dissolve in a small volume, it is easier to dilute than to concentrate DNA.