Rapid Elution of DNA from Agarose Gels
Making the glass wool filter column.
Using a clean hypodermic needle, drive a hole in the end of a 650 ul eppendorf tube from the inside.
Wearing gloves, pull off a small piece of glass wool and roll it into a ball between hands. Place the glass wool plug in the bottom of the 650 ul tube. You may need to use a dowel to pack the glass wool in the bottom of the tube. Do not cut the glass wool, as this may produce small glass fibers that can pass through the hole in the small tube.
Place the tube with the glass wool in a 1.7ml eppendorf tube with the top cut off. This completed spin column is now ready for use.
Eluting DNA from agarose gel fragments.
Visualize ethidium bromide stained agarose gel with a transilluminator on low setting. Working quickly to minimize UV exposure to the DNA, excise the fragment of interest with a clean razor blade or microscope cover slip. Place the agarose fragment in the spin column.
Centrifuge the tube at full speed for 30 seconds to elute the DNA. Spinning longer coelutes substances that are inhibitory to further enzymatic reactions.
The eluted DNA can now be used directly in enzymatic reactions. For ligations, no more than 40% of the total reaction volume should be eluted DNA, as this reduces ligation efficiencies.
The DNA fragments can be further purified by ethanol precipitation. The addition of 2-4 ug of carrier tRNA prior to precipitation can increase yield, and its presence in ligation reactions is non-inhibitory.