Recovery of plasmids in an aqueous two-phase system

1. A method for the purification of plasmid DNA in an aqueous two-phase system, comprising:

(a) providing a composition including a first polymer EO 50 PO 50 , a second polymer Dextran T 500 and, optionally, a salt;

(b) contacting said composition with an aqueous solution comprising plasmid DNA and RNA to form a mixture which contains from about 4.5% (w/w) EO 50 PO 50 /4.5%(w/w) Dextran T 500, to about 2.5%(w/w)EO 50 PO 50 /9% (w/w) Dextran T 500;

(c) providing a phase separation wherein plasmid DNA is partitioned to a top aqueous phase while RNA partitions predominantly to a lower phase, and subsequently isolating the top aqueous phase;

(d) increasing the temperature of the isolated top aqueous phase to a temperature above the cloud point of the first polymer and below a temperature where plasmid DNA is degraded and subsequently isolating a top aqueous phase so formed; and, optionally,

(e) performing a chromatography step to recover the plasmid DNA from the isolated top phase of step (d).

2. The method of claim 1 , wherein the amount of the first polymer is about 4.5%(w/w) and the amount of the second polymer is about 4.5%(w/w) of the mixture in step (b).

3. The method of claim 1 , wherein the aqueous solution that includes plasmid DNA is a cell lysate, and wherein said method further comprises a step for desalting the cell lysate before step (b).

4. The method of claim 1 , wherein the contacting according to step (b) involves mixing at room temperature.

5. The method of claim 1 , wherein the isolation according to step (c) and/or step (d) is by centrifugation.

6. The method of claim 1 , wherein the salt concentration in said composition in step (a) is at least ten times above that of the aqueous solution.

7. The method of claim 2 , wherein the salt concentration in said composition in step (a) is at least ten times above that of the aqueous solution.