Mike's hints for successful minipreping.

1. Always, always, always mark each culture tube in an unambiguous manner (with a sharpie pen).
2. Always, always, always mark each collection and final collection tube in an unambiguous manner (with a sharpie pen). These should correspond to your cultures - all unmarked tubes look identical.
3. If you fail to recover plasmid, the most likely cause is that you failed to add ampicillin or that your ampicillin was bad. Repeat using a fresh stock of (100mg/ml) ampicillin.
4. Always check minipreps by running out 2-4 µL on an 0.5 to 1% agarose gel before setting up restriction digests, etc

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Protocol  Zhou et al 1990 as modified by Tamara Basta

1. Grow up single colony in 5ml LB + 50 ug/ml antibiotic (generally diluted from 100 mg/ml ampicillin stock). Place in rotator overnight in 37ªC room / incubator.
2. Spin ~1.5 ml of an overnight bacterial culture for 1 min., remove supernatant and add another ~1.5ml of culture, leaving the original bacterial cell pellet undistrubed.
3. Gently decant supernatant - leave ~50µL of supernatant with the cell pellet - you can use Empirical miniprep kit.  → follow this link. 
4. Resuspend by running tube along tube rack (Alberto's Trick)
5. Add 300 µL of TENS (lysis buffer) and mix by inversion* until completely lysed -- make up TENS buffer fresh from 10 x stocks (see below).
6. Add 150 µL 3.0 M sodium acetate, pH 5.2 and invert to mix*
7. Centrifuge for 5 minutes pellet cellular debris and chromosomal DNA
8. Transfer supernatant to fresh microfuge tube
9. Add 0.9 mL -20°C 100% ethanol
10. Spin for 5 minutes at 4°C to pellet plasmid DNA
11. Discard supernatant and rinse pellet twice with 70% ethanol
12. Dry pellet in speed-vac for ~5 minutes
13. Resuspend pellet in 50-100 µL in resuspension buffer (you can add RNAase at this step).

* do not vortex at these steps, it will shear the chromosomal DNA

TENS Buffer:  TE + 0.1N NaOH and 0.5% SDS from 10X TE, 5N NaOH and 20% SDS

Qiagen miniprep

1. Grow up single clone in 5ml LB + appropriate antibiotic
2. Centrifuge 1.5 ml of an overnight bacterial culture for 1 min. (double if the culture is growing slowly)
3. Gently decant supernatant - resuspend cell pellet in 250 μL P1 buffer + RNase
4. Resuspend by running tube along tube rack (Alberto's Trick)
5. Add 250 μL Buffer P2 and mix thoroughly (but gently) by inverting the tube 4–6 times until the solution becomes viscous + clear. Do not vortex.
6. Neutralize by adding 350 μl Buffer N3 and mix immediately by inverting the tube several times.
7. In microfuge, spin for 10 minutes to pellet cellular debris and chromosomal DNA
8. Transfer the supernatant the blue QIAprep spin column, avoid disturbing the pellet - spin 1 minute
9. Discard flow through - wash column with 0.75 ml Buffer PE – centrifuge for 1 min.
10. Discard the flow through, spin again for 1 minute
11. Place the QIAprep column in a clean 1.5 ml microcentrifuge tube
12. Elute DNA into the clean tube by adding 50 μL EB Buffer (10 mM Tris·Cl, pH 8.5) to the center of QIAprep spin column, let stand for 1 min, and centrifuge for 1 min -
13. To check plasmid - run out 1-2 μL on agarose gel.