Size fractionation of double-stranded DNA by precipitation with polyethylene glycol.

We show that DNA molecules of differing molecular mass are separable by selective precipitation with polyethylene glycol (PEG+.. Higher molecular mass DNA precipitates at lower PEG concentrations than lower molecular mass DNA. Double-stranded DNA can be fractionated at least in the range of 3 times 10-7 to 1 times 10-5 daltons. The effects on PEG concentration, sodium chloride concentration, DNA concentration, pH, divalent ions, precipitation time, and centrifugal force have been determined. These studies show PEG precipitation offers a size fractionation method for DNA which is convenient, of high capacity, and applicable over a wide range of conditions. However, resolution is not high and separation of two species approaches 100% only if they differ in molecular mass by at least a factor of two.