Lane:MagneticPlasmidPrep

Overview

This is an (as yet untested) work-in-progress protocol with the goal of replacing silica columns for bacterial minipreps with a magnetic bead based protocol. The starting point is ref. [1]; the protocol is based on this. It may be possible to simplify the cleared lysate generation to a protocol more similar to that of Zymo's direct-from-culture lysis. The major predicted advantage of this protocol over spin-column protocols is cost; beads are ~$380 for enough for 3,750 purifications, or ~10c per purification. Whether the yield and purity match that of a spin column is unclear.

Materials

• Solution 1 (Uses 30µl/prep - make 10ml; store at RT or at 4˚C to preserve RNAse A if preferred):
  • 50mM Glucose
  • 25mM Tris pH 8.0
  • 10mM EDTA pH 8.0
  • 100µg/ml RNAse A

• Solution 2 (Uses 60µl/prep)
  • 0.2N NaOH
  • 1% SDS

• Solution 3 (Uses 45µl/prep)
  • 3M KOAc

• W1 (Uses 1ml per prep)
  • 5M NaCl

• W2 (Uses 500µl per prep)
  • 25mM Tris Acetate pH 7.8
  • 100mM KOAc
  • 10mM Mg2OAc
  • 1mM DTT

• 2X Binding buffer (uses 100µl per prep)
  • 20% PEG 8,000
  • 2.5M NaCl

Procedure

Preparing magnetic bead stock

Carboxy-coated magnetic beads are Sera-mag SpeedBeads (Fisher #09-981-123). These come at 50mg/ml; protocol calls for 20mg/ml in 0.5M EDTA pH7.2:

1. Mix 400µl Sera-mag stock and 600µl ddH₂O
2. Collect beads on magnet.
3. Remove supernatant
4. Resuspend beads in 1ml 0.5M EDTA pH 7.2.
5. Place tube back on magnet. Remove supe.
6. Resuspend beads in 1ml 0.5M EDTA pH 7.2 again.

Store at 4˚C.

Purifying DNA:

1. Spin down 1 ml bacterial culture.
2. Resuspend pellet in 30µl Solution 1.
3. Add 60µl Solution 2. Mix by inversion, make snot, incubate for a minute or two. More than five minutes is reported to permanently damage DNA.
4. Neutralize with 45µl Solution 3; mix by inversion.
5. Spin at max speed in room-temp microfuge for 10 minutes. Transfer 100µl of the supernatant (cleared lysate) to a new tube; trash the pellet.
6. Add 10µl of your prepared magnetic beads to the cleared lysate along with 100µl 2X binding buffer. Incubate at RT for 5 minutes.
7. Using magnetic rack, wash the beads with 500µl W1 twice. During washes, beads can be left as a pellet on the side of the tube. No need to resuspend.
8. Wash once with 500µl W2.
9. Resuspend beads in 50µl ddH₂O. Spin to the bottom of the tube in a minifuge (givining ~1 min for DNA to be released from beads), then place back on rack. Collect the water containing DNA.

Notes

Please feel free to post comments, questions, or improvements to this protocol. Happy to have your input!

1. '''*~~~~''': There are some things about the buffers that might be worth experimenting with. Buffer W2 is a little unexpected; why so complex (Mg, DTT)? Could it be replaced with 70% or 80% EtOH or as in Agencourt Ampure XP protocols? This would necessitate significant drying time to remove EtOH, though.

Please sign your name to your note by adding '''*~~~~''': to the beginning of your tip.

References

Relevant papers and books

1. Goldbeter A and Koshland DE Jr. An amplified sensitivity arising from covalent modification in biological systems. Proc Natl Acad Sci U S A. 1981 Nov;78(11):6840-4. DOI:10.1073/pnas.78.11.6840 |

Contact

• Who has experience with this protocol?

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