One Shot™ Mach1™ T1 Phage-Resistant Chemically Competent E. coli

We would recommend a mcr/mrr- strain, which prevents restriction of methylated eukaryotic DNA in the E. coli host. We would also recommend using a T1R strain, as T1 is a common contaminant in genomic/cDNA libraries.

Our Mach1-T1R competent cells grow faster than any of our common cloning strains. It has a doubling time of 54 minutes versus doubling times in excess of 70 mins for standard cloning strains, such as DH5α cells. Colonies of Mach1-T1R begin to be visible on a plate 8 hours after plating the transformation mix at 37 degrees C. It can be mini-prepped from 1.5 mL cultures in as little as 4 hours at 37 degrees C after inoculation with a single large overnight colony.

There are other strains available that may function similarly to Stbl2 cells in stabilizing inserts or vectors with repeated DNA sequences. However, one advantage of Stbl2 cells over many similar strains is that they are sensitive to Kanamycin, so you can use Stbl2 to propagate plasmids containing a Kanamycin resistance marker. 

For best results, DNA used in electroporation must have a very low ionic strength and a high resistance. A high-salt DNA sample may be purified by either ethanol precipitation or dialysis.

The following suggested protocols are for ligation reactions of 20ul. The volumes may be adjusted to suit the amount being prepared.

Purifying DNA by Precipitation: Add 5 to 10 ug of tRNA to a 20ul ligation reaction. Adjust the solution to 2.5 M in ammonium acetate using a 7.5 M ammonium acetate stock solution. Mix well. Add two volumes of 100 % ethanol. Centrifuge at 12,000 x g for 15 min at 4C. Remove the supernatant with a micropipet. Wash the pellet with 60ul of 70% ethanol. Centrifuge at 12,000 x g for 15 min at room temperature. Remove the supernatant with a micropipet. Air dry the pellet. Resuspend the DNA in 0.5X TE buffer [5 mM Tris-HCl, 0.5 mM EDTA (pH 7.5)] to a concentration of 10 ng/ul of DNA. Use 1 ul per transformation of 20 ul of cell suspension.

Purifying DNA by Microdialysis: Float a Millipore filter, type VS 0.025 um, on a pool of 0.5X TE buffer (or 10% glycerol) in a small plastic container. Place 20ul of the DNA solution as a drop on top of the filter. Incubate at room temperature for several hours. Withdraw the DNA drop from the filter and place it in a polypropylene microcentrifuge tube. Use 1ul of this DNA for each electrotransformation reaction.

Many media can be used to grow transformed cells, including standard LB, SOB or TB broths. However, S.O.C. is the optimal choice for recovery of the cells before plating. The nutrient-rich formula with added glucose is often important for obtaining maximum transformation efficiencies.