DNA extraction from agarose gels (Dialysis-tubing)

Contributed by Matt Lewis <hop2kin@yahoo.co.uk>

Dialysis tubing (semi-permeable membrane, Visking tubing)

• Freeze the gel slice at –20C for 30 minutes.

This is to make it easier to handle the gel slice

• Cut a 5cm length of dialysis tubing and rinse it inside and out with distilled water. Then rinse it with the same buffer used for the gel (eg. 0.5 x TBE) and leave it submerged in a small beaker of this buffer. Seal one end with a dialysis clip

Dialysis tubing (Sigma D9777) is purchased in rolls (dried), prepared by boiling and stored submerged in buffer at 4C. Dialysis clips are Sigma Z37,096-7.

• Insert the frozen gel-slice into the tubing and add 200–400µL of buffer (eg. 0.5 x TBE). Seal the other end of the tubing with a second dialysis clip.

The buffer around the gel-slice must be the same as the buffer inside the gel

• Immerse the sealed tubing in an electrophoresis tank so that the DNA band is parallel to the electrodes and apply 5V/cm electric field.

The DNA will migrate out if the gel towards the positive electrode. It will be retained by the dialysis tubing. You can see this happening under long-wavelength UV if you like. It takes about 10–15 minutes.

• Remove the buffer from the tubing and place into a 1.5mL microfuge tube.
• Phenol/chloroform extract and ethanol precipitate the DNA. Re-dissolve the DNA pellet in an appropriate volume of water or TE buffer (e.g. 10µL).

*The pellet is often so small that it is invisible *

This method is based, with permission, on an original protocol available here.