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17-6-11
Making competent cells:
Competent DH5alpha cells were made and transformed with the following adapted protocol of Robyn Eilander (MolGen Groningen):
Materials to be supplied by the user
• 1.5 ml microcentrifuge tubes (sterile, dry, 4 °C, min. 200 pieces)
• 50 ml plastic centrifuge tubes (sterile, pre-cooled, 8 pieces)
• cuvettes
• 2 L flask (sterile, 2 flasks)-preferably Erlenmeyers
• stove, 37 °C
• TY broth (sterile, 5 ml)
• 2xTY broth (sterile, 37 °C, 500 ml)
• TY agar plate
• E. coli strain from glycerol stock
• Buffer RF1 (ice cold)
• Buffer RF2
• ice
• liquid nitrogen
Buffer RF1 500mls
Rubidium chloride 6.00 g
Potassium acetate 2.45 g
Calcium chloride 2H20 0.75 g
Glycerol 75.00 g
Adjust to pH 5.8 using 0.2 M Acetic acid
Sterilise by filtration
Buffer RF2 300mls
0.5 M MOPS PH 6.8 6.00 ml (Use 4 M NaOH to pH MOPS)
Rubidium chloride 0.36 g
Calcium chloride 2H20 3.30 g
Glycerol 45.00 g
Adjust to pH 6.8 with 1M NaOH
Sterilise by filtration
Protocol
Day 1
1. Streak out E. coli strain, direct from a glycerol stock 24 hours before you intend to put up an overnight
culture.
2. Autoclave 200 1.5 ml microcentrifuge tubes and ensure they are dry before use. (Leave the dry tubes at 4 °C so
they are pre-cooled before use.)
Day 2
1. ~5pm day before growing cultures, inoculate 5 ml 2xTY with a freshly grown colony. Grow O/N at 37 °C.
2. It is a good idea to put 2x 2 litre sterile flasks & 500 ml sterile 2xTY at 37 °C overnight – this will create
continuity of temperature when you inoculate your 2x 200 ml cultures the next morning.
Day 3
1. Add 200 ml pre-warmed 2xTY into a 2 litre flask. Inoculate with 2 ml (1/100 dilution) of the overnight
culture. Grow 2x 200 ml cultures at the same time. Grow cultures to an OD600nm of between 0.3-0.4.This should
take a maximum of 2 hours.
2. Put 8x 50 ml plastic centrifuge tubes in ice to pre-cool. Make sure your centrifuge has been pre-run to bring
down the temperature to 4 °C.
3. Collect culture into 8 x 50ml pre-cooled centrifuge tubes. Leave on ice for 15 minutes.
4. Pellet the cells by centrifuging at 2700 rpm for 15 minutes 4 °C.
5. Remove the supernatant. Drain residue supernatant from the cell pellets. Do this by turning the tubes upside
down on paper towels. Remove the supernatant left on the tube lip and inside wall using tissue. Put the tubes
back on ice.
6. Resuspend cell pellets by adding 16 ml of ice cold RF1 to each pellet and vortexing gently. (Do this just
enough to resuspend the cells quickly). Return the tubes to ice for 15 minutes.
7. Pellet the cells by centrifuging at 2700 rpm for 15 minutes 4 °C.
8. Remove the supernatant. Drain residue supernatant from the cell pellets. Do this by turning the tubes upside
down on paper towels. Remove the supernatant left on the tube lip and inside wall using tissue. Put the tubes
back on ice.
9. Add 4 ml of RF2 to each cell pellet. Gently resuspend each pellet. Leave the resuspended pellets on ice for 15
minutes.
10. Get some liquid nitrogen.
11. Dispense 4 ml of resuspended cell pellet in aliquots of 200 μl to each 1.5 ml microcentrifuge tubes (can use
a dispenser pipette). After aliquoting 4 ml from one tube shut the lids on the 1.5 ml tubes and flash freeze in
liquid Nitrogen. Repeat this process with all 8 resuspended cell pellets.
Store the frozen aliquots of competent cells at -80 °C.
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