Joyce: DNA precipitation

Procedure

1. Add enough 3M NaOAc pH 5.2(or equivalent) to make the final volume 0.33 M
2. Add 2 volumes of 99% EtOH
3. Place at -70°C for at least 30 minutes
4. Spin at 14K (?) at 4°C for 30 minutes
5. Pipette off supernatant (don't disturb the pellet)
6. Wash (gently invert tube 3-4 times) with 300 ul 80% EtOH
7. Spin at 14K for 2 minutes
8. Pipette off supernant (don't disturb the pellet)
9. Spin down residual EtOH and remove by pipetting
10. Air dry for 20 minutes at 37°C, dessicate or speed vac it
11. Resuspend in sterile water or TE

Notes

• To make the final volume of NaOAc 0.33 M, use 1/10th of the final volume. For instance, if I have 90 ul of a DNA solution, use 10 ul of the 3 M NaOAc to make a final concentration of 0.33 M.
• KOAc apparently helps precipitate SDS better than NaOAc, so use KOAc when you have a DNA solution that's dirty with SDS
• Placing the solution at -70°C for a longer time will help precipitate smaller (less than 500 bp) DNA fragments
• The pellet will stick strongly to the ependorff wall after treatment with 99% EtOH, but will stick less when using 80% EtOH (because DNA is more soluble in water), so be careful when pipetting off the 80% EtOH not to disturb the pellet
• Organic solvents like EtOH can inhibit downstream reactions (some REs are more sensitive to ethanol than others, for instance), so be sure to pipette off as much as possible using a P10-type tip, and allow the ethanol adequate time to evaporate