Transforming chemically competent cells (Inoue)

Also see Preparing chemically competent cells (Inoue)

Method

1. Thaw 25 - 200 μl TB buffer cells on ice. Do not use glass tubes, which adsorb DNA.
2. Add DNA, pipette gently to mix (keep volume of DNA less than 5% of the cell volume)
3. Incubate on ice for 30 minutes
   • Note: If you are in a rush, you can shorten this incubation time to 5-10 min.
4. Incubate cells for 30 seconds at 42°C.
5. Incubate cells on ice for 2 min.
6. Add 4 volumes of room temperature SOC (not critical)
7. Incubate for 1 hour at 37°C on shaker.
   • Note: Can also save some time here by reducing incubation to ~45 min.
   • Note: Step can be eliminated if plating on Amp plates, but not most other antibiotics
8. Spread 100-300 μl onto a plate made with appropriate antibiotic.
9. Grow overnight at 37°C.

Experimental results

First attempt varied several parameters: incubation time on ice prior to heat shock, heat shock length, addition of DTT at 20mM.

• DTT appeared to have little effect when added during transformation.
• Incubating for 1/2 hour on ice had a positive effect, perhaps 1.5 to 2x efficiency gain.
• Heat shock of 0 or 15 s rather than 30 s reduced efficiency about 8x
• Heat shock at 30 s or 60 s gave approximately similar results. (*Edit: 50s is preferable)

Achieved efficiency was 3 x 10⁷ per microgram. A control transformation with Invitrogen cells was at 1.2 x 10⁸ per microgram.