DH5α Competent Cells
Protocol for Preparation of DH5α Competent Cells
Day 1
Step 1
Streak DH5α for isolation on LB plate (no ampicillin).
Step 2
Grow at 37 ˚C.
Day 2
Step 3
At the end of the day, add a single colony to a 4-16 ml (4 ml for 1X, 16 ml for 4X) SOB media aliquot for overnight culture at 37 ˚C and 250 rpm.
Day 3
Step 4
Add 4.0 mls overnight culture to 400 ml SOB in 2L flask. Grow at 37 ˚C and 250 rpm until OD550 = 0.4-05 (2-3 hours). Transfer to conical 250 ml Tubes.
Step 5
Chill 5-10 min on ice.
Step 6
Spin at 3-4k for 10 min. Pour off sup.
Step 7
Resuspend cell pellet by pipetting in 150 ml TFB I. Ice for 5 min
Step 8
Spin at 3-4k for 10 min at 4 ˚C. Pour off sup.
Step 9
Gently resuspend in 15 ml TFB II (if > 1X pool together, e.g. 60 ml for 4X). Ice for 15 min
Step 10
Aliquot 50 ul to prechilled sterile 0.5 ml microcentrifuge tubes. Snap freeze in matrix of dry ice crushed to powder. Bacteria are ready for transformation.
Media/Buffers
SOB Media
TFB I
TFB II
0.25 M KCl (F.W. = 74.55)
1.86 g KCl/100 ml H2O. Filter sterilize.
2M MgCl (Hexahydrate = F.W. 203.3)
40.66 g MgCl2 to 100 ml. Filter sterilize.
