EtOH ppt of DNA in Urea

Shahram Mori smori at
Wed Nov 29 21:41:39 EST 1995

Duke Groebe (drg at wrote:
: I'm attempting to precipitate short DNA oligos (68-mer) from a solution
: containing 7 M urea.  I added glycogen to 30 ug/ml, Na acetate to 0.3 M,
: and 3 volumes of ethanol.  I got a goopy clear ppt upon centrifugation and
: washing that I suspect is residual urea.  A review of relevant literature
: was not very helpful.  Any suggestions/insights that might help me
: resolve/avoid this situation would be greatly appreciated.  Respond here or
: by e-mail (drg at

: Thanks,

: Duke

If you think it might be the Urea that's affecting your pptation, why not 
dialyze it away? Try dialyzing vs TE 4 or 5 times. Maybe more. The 
concentration of urea in your solution is pretty high.
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Shahram Mori
Program in Molecular Biology
Department of Chemistry and Biochemistry Box 3C
New Mexico State University
Las Cruces NM

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