PEG/NaCl ppt. of PCR products

David F. Spencer dspencer at
Mon Dec 15 15:47:46 EST 1997

In article <66pei2$8g8_001 at>, BGYCSW at (C.S. Wilding)

> Is there a lower cut-off point for PEG/NaCl 
> precipitation of PCR products prior to sequencing (as 
> referred to in Current Protocols). I usually use it for 
> 600-1000bp products and it is OK but failed in an effort 
> on 120-180bp products. Is the method unsuitable in this 
> instance?
> Craig. (BGYCSW at LEEDS.AC.UK)

The characterization of PEG precipitation is in :

Lis and Schleif, Size fractionation of double-stranded DNA by precipitation
with polyethylene glycol. Nucleic Acids Research 2(3):383-389 (1975).
[Note that the figure legends for Fig.1 and 2 are reversed]

According to their observations if you use PEG at 12% (w/v) final and NaCl
at 1.1 M final you can PEG precipitate down to 80 bp but there are also an
effect on the time of incubation at 4C. With PEG at 12% but NaCl at .55 M
the low cutoff was 125 bp.


David F. Spencer, PhD
Dept. Of Biochemistry
Dalhousie University
Halifax, Nova Scotia

dspencer at
dspencer at

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