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Purifying DNA fragments using glass beads

From gel:

  • weigh gel slice
  • add 3 x weight in mg of 6 M NaI
  • melt in 55 C waterbath for about 5 minutes. Check and mix every 2 minutes or so. Make sure that gel has completely melted before next stage, but don't leave at 55 C any longer than necessary.

From liquid:

  • add 3 x volume of 6 M NaI.

In both cases:

  • add 5 ul glass bead suspension (make sure glass beads are well suspended before taking 5 ul). Mix and leave on ice for at least 10 minutes.
  • spin briefly (30 seconds to 1 minute). Remove supernatant and discard.
  • add 0.25 ml ice-cold wash buffer (stored in freezer). Respin, remove and discard supernatant.
  • repeat the previous step twice more (total of 3 washes). After the last wash, remove as much wash buffer as possible from the bead pellet.
  • resuspend pellet thoroughly (by pipetting up and down) in 15 ul of EB buffer.
  • return to 55 C waterbath for 10 minutes, mixing again (by flicking) after 5 minutes or so.
  • spin out glass beads and transfer supernatant (containing DNA) to a fresh tube.

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