E coli Chemical Transformations
Transformation of competent E. coli cells
We use OneShot TOP10 Chemically competent E. coli cells (comparable to DH5α) or home-made competent cells that are to be found in the -80°C freezer (Parsch freezer).
When using commercial cells, for each transformation, we use 25μl. Each tube in the -80 can thus be used for 2 transformations.
Do transformation using the long version of the manufacturer’s protocol:
- Thaw the cells on ice (and split over 2 tubes to get 25μl cells, do not pipette more than once as cells are very sensitive).
- Add DNA to the cells:
- Flick and place back on ice for 30 min
- Heatshock the cells for 60sec at 42°C
- Place back on ice for 2 min
- Add 250μl 37°C SOC or LB (without antibiotic)
- Incubate these tubes with shaking at 37°C for 1 hour for ampicillin marker or 75-90min for kanamycin.
- Preheat LB plates with appropriate antibiotic (50 μl Ampicillin 100mg/ml stock or 25 μl Kanamycin 50mg/ml stock) to 37°C.
- add 40 μl X-Gal (freezer 7 top drawer) when blue white screening (e.g. using TOPO cloning) is required
- Spread the 100 μl cells on the preheated LB+amp plates and incubate overnight at 37°C.
- the rest of the cells can be left in the fridge to plate out the next day if needed (e.g. when too many or too few colonies were obtained).
- After one day the plates should show colonies