DNA precipitations

Chris Boyd chrisb at hgu.mrc.ac.uk
Thu Feb 1 07:51:23 EST 1996

David Plotner (dplotner) wrote:
: Does anyone know of potential differences/problems between the 
: conventional methods of DNA precipitation in EtOH. In particular, how do 
: NaCl, NaOAc, and ammonium acetate compare?

The following short paper discusses the classic EtOH/NaOAc
precipitation and variations thereon:

  author =       "Wallace, D. M.",
  title =        "{Precipitation of nucleic acids}",
  journal =      "Methods Enzymol.",   
  volume =       "152",
  pages =        "41--48",
  year =         "1987",

However, you can disregard the advice to chill DNA for extended periods
of time in the presence of EtOH except when precipitating very small
amounts (in which case of course you'll use a carrier anyway).  I
routinely leave the samples on ice for 15' -- 30', then spin for 30' at
4 C. If there is a lot of DNA (above say 100ng/ul), there is no need
for chilling at all.  As a (slightly pessimistic) rule of thumb, I
expect to lose 50% of the DNA on precipitation, even with carrier.

Best wishes,
Chris Boyd          | from,  \MRC Human Genetics Unit / Western General Hospital
chrisb at hgu.mrc.ac.uk| not for \        Crewe Road / Edinburgh EH4 2XU / Scotland

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