Biology Protocols

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Purification of DNA from Agarose by Electrophoresis

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  • Run an analytical gel of suitable percentage in TAE or TBE buffer with ethidium bromide.
  • Cut out the required band on the longwave transiluminator.
  • Clip a piece of pre-prepared and rinsed dialysis tubing at one end. Cut the tubing to a length that is holdable but not excessively long.
  • Squeeze out any water and pipette in 200-600μl of TAE buffer without ethidium bromide (unless your band is very small use 600μl).
  • Insert the agarose slice and position it parallel to the wall of the tubing and carefully squeeze out any bubbles. Clip the tubing just above the gel slice.
  • Place the tubing horizontally on a tray and return it to the tank which has been filled to just above the level of the tray with TAE or TBE without ethidium bromide.
  • Electrophorese at 90V for 1 hour.
  • Check the bag on the longwave transilluminator. The DNA should be a bright band stuck on the inner surface of the tubing.
  • Return the bag to the tank, reverse the polarity and electrophorese at the same voltage for 30 seconds.
  • Using a 200µl pipette, remove all the buffer from around the gel.
  • Check the bag on the transilluminator. All the fluorescence should have gone and should be seen in the eppendorf tube containing the removed buffer.
  • Make the solution 0.3M with NaCl and ethanol precipitate overnight at -20°C.


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