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MW of PEG for Purification of DNA - (Jun/28/2012 )


I'm following the Cold Spring Harbor labs' protocol for PEG purification of DNA. The PEG-MgCl2 solution they describe is as follows (from http://cshprotocols....06/1/pdb.rec382)

40% (w/v) polyethylene glycol (PEG 8000)
30 mM MgCl2

Dissolve 40 g of PEG 8000 in a final volume of 100 ml of 30 mM MgCl2. Sterilize the solution by passing it through a 0.22-μm filter, and store it at room temperature.

However, I only have PEG of MW 3350 in the lab, not PEG of MW 8000. Will it still work with PEG 3350?
Why/why not? I don't know how PEG works to precipitate DNA and I would really appreciate it if someone who knew explained it to me.




it's been my experience that peg 3350 is not a good replacement for peg 8000, but i was not using it to precipitate dna.

you can use peg 6000, if you have it, it is the same as peg 8000 (peg 6000 was renamed peg 8000).


Basically as far as I can tell, the PEG acts as a molecular sieve - the higher the concentration, the smaller the fragments that are retained in the solution.

You may be able to use PEG 3350, but you would have to determine the concentration for effective use empirically, and I suspect that this would lead to PEG solubility issues before you got to an effective concentration.