Lidstrom:Miniprep

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Tips You (Mostly) Won't Find in the Manual

• Use 1 colony in 2 mL of TB +antibiotic grown overnight.
  • TB gives you a higher plasmid yield than LB, but our lab currently doesn't make it (Janet 2/23/12). If your plasmid is high-copy number, one tube is sufficient. If you have a medium copy plasmid, grow 2-3 cultures from the same colony in parallel and pool them before loading the column.

• If nuclease activity is a problem, wash with Quiagen's PB buffer.
  • Buffer PB contains a high concentration of guanidine hydrochloride and isopropanol. The exact composition of Buffer PB is confidential. However, this buffer can be purchased separately.

• Elute in water, not the elution buffer that comes with the kit.
  • The elution buffer stabilizes DNA and reduces DNase activity, but comes at a cost -- the added chemicals are likely to lessen DNA sequencing and subsequent DNA manipulation successes.

• The amount of time the overnight culture grows is quite flexible.
  • There is literature that suggests what stage in growth is optimal to harvest plasmids. People usually just do whatever is convenient.

Expected Yield

• 2 mL of pSB1A3 (high copy) should yield ~ 150 ng/uL in 30 uL.
• 4 mL pSB3K3 (medium copy) culture should yield ~ 30 ng/uL in 30 uL
  • Make sure the air:liquid ratio is at least 5:1

Miscelaneous

• Our lab prefers the Fermentas/Thermo Scientific miniprep kit over Quiagen because itis cheaper. -Janet 10/2012
• Do not grow cultures with less than 4:1 air:liquid ratio -- it is very bad for plasmid prep. This is still one of Janet's open questions 2/23/12
• You can elute in 30uL instead of 50uL to get a more concentrated sample.
• Record the A260/A280 measurement down when you record the concentration. It should be between 1.8 and 2.
• You can leave the cap on the fresh eppendorf tube you elute in. This allows you to pre-label the tube and stick it straight into the freezer after you are done instead of pipetting each into a fresh tube.