Competent Cell Selection Guide

Find more protocols and selection guides in the Molecular Biology Guide.

Sigma-Aldrich offers a range of Escherichia coli bacterial cells made competent by optimized procedure specific to each strain, involving strain verification and efficiency testing. Our current competent cells are being discontinued; soon we will offer a wider variety of competent cells with higher transformation efficiency.

Application Product No. Product Description Transformation Efficiency Genotype Blue White Screening Capable
for protein expression and DNA plasmid production CMC0001 SIG10 Chemically Competent Cells ≥ 1 × 108 F- mcrA Δ(mrr-hsdRMS-mcrBC) endA1 recA1 Φ80dlacZΔM15 ΔlacX74 araD139 Δ(ara,leu)7697 galU galK rpsL nupG λ- tonA Y
for protein expression and DNA plasmid production CMC0002 SIG10 F' Chemically Competent Cells ≥ 5 × 108 [F´ pro A+B+ lacIqZΔM15::Tn10 (TetR)] /mcrA Δ(mrr-hsdRMS-mcrBC) endA1 recA1 Φ80dlacZΔM15 ΔlacX74 araD139 Δ(ara, leu)7697 galU galK rpsL nupGλ tonA Y
for protein expression and DNA plasmid production CMC0003 SIG10 HIGH Electrocompetent Cells ≥ 5 × 109 F- mcrA Δ(mrr-hsdRMS-mcrBC) endA1 recA1 Φ80dlacZΔM15 ΔlacX74 araD139 Δ(ara,leu)7697galU galK rpsL nupG λ- tonA (StrR) Y
for protein expression and DNA plasmid production CMC0004 SIG10 MAX Electrocompetent Cells ≥ 2 × 1010 F- mcrA Δ(mrr-hsdRMS-mcrBC) endA1 recA1 Φ80dlacZΔM15 ΔlacX74 araD139 Δ(ara,leu)7697galU galK rpsL nupG λ- tonA (StrR)  Y
for general cloning & library production CMC0005 SIG10 F' MAX Electrocompetent Cells ≥ 2 × 1010 [F´ pro A+B+ lacIqZΔM15::Tn10 (TetR)] /mcrA Δ(mrr-hsdRMS-mcrBC) endA1 recA1 Φ80dlacZΔM15 ΔlacX74 araD139 Δ(ara, leu)7697 galU galK rpsL nupG λ- tonA (StrR)  Y
for general cloning & library production CMC0006 SIG10 ULTRA Electrocompetent Cells
≥ 4 × 1010 F- mcrA Δ(mrr-hsdRMS-mcrBC) endA1 recA1 Φ80dlacZΔM15 ΔlacX74 araD139 Δ(ara,leu)7697galU galK rpsL nupG λ- tonA (StrR)  Y
for general cloning & library production CMC0007 SIG10 5a Chemically Competent Cells ≥ 1 × 108 fhuA2Δ(argF-lacZ)U169 phoA glnV44 Φ80 Δ(lacZ)M15 gyrA96 recA1 relA1 endA1 thi-1 hsdR17 Y
for plasmid production using unstable DNA CMC0008 STEADY Chemically Competent Cells > 1 × 107 recA13 supE44 ara-14 galK2 lacY1 proA2 rpsL20(StrR) xyl-5 λ– leu mtl-1 F– mcrB mrr hsdS20(rB–, mB–) N
for plasmid production using unstable DNA CMC0009 STEADY Electrocompetent Cells > 1 × 107 recA13 supE44 ara-14 galK2 lacY1 proA2 rpsL20(StrR) xyl-5 λ– leu mtl-1 F– mcrB mrr hsdS20(rB–, mB–) N
for making Uracil-containing DNA for mutagenesis CMC0010 CHANGER Electrocompetent Cells 1 × 109 [F’ Tra+ Pil+ (CamR)] ung-1 relA1 dut-1 thi-1 spoT1 mcrA N
for BAC & cosmid cloning CMC0011 XLDNA V2 Electrocompetent cells
≥ 1 × 1010 F- mcrA Δ(mrr-hsdRMS-mcrBC) endA1 recA1 Φ80dlacZΔM15 ΔlacX74 araD139 Δ(ara,leu)7697 galUgalK rpsL nupG (attL araC-PBAD-trfA250 bla attR) λ- Y
for BAC & cosmid cloning CMC0012 XLDNA SIG10 Electrocompetent cells ≥ 1 × 1010 F - pro A+B+ lacIqZΔM15::Tn10 (TetR)] /mcrA Δ(mrr-hsdRMS-mcrBC) endA1 recA1 Φ80dlacZΔM15 ΔlacX74 araD139 Δ(ara, leu)7697 galU galK rpsL nupG λ- tonA (StrR) N
for production of biotinylated proteins CMC0013 BIOTINYLATER F' Electrocompetent Cells >1 ×1010 MC1061 [F´ pro A+B+ lacIqZΔM15::Tn10 (TetR)] araD139 ∆(ara-leu)7696 ∆(lac)l74 galU galK hsdR2(rΚ- mΚ+) mcrB1 rpsL (StrR) birA N
for protein expression CMC0014 BL21(DE3) Chemically Competent Cells ≥ 1 × 107 F – ompT hsdSB (rB- mB-) gal dcm (DE3) N
for protein expression CMC0015 BL21(DE3) pLysE Chemically Competent Cells ≥ 1 × 107 F – ompT hsdSB (rB- mB-) gal dcm (DE3) N
for protein expression CMC0016 BL21(DE3) Electrocompetent Cells
≥ 5 x 109 F – ompT hsdSB (rB- mB-) gal dcm (DE3) N
for the highest protein expression CMC0017 OverExpress C41(DE3) Chemically Competent Cells ≥ 1 × 106 F – ompT hsdSB (rB- mB-) gal dcm (DE3)  N
for the highest protein expression CMC0018 OverExpress C41(DE3) pLysS Chemically Competent Cells ≥ 1 × 106 F – ompT hsdSB (rB- mB-) gal dcm (DE3) pLysS (CmR) N
for the highest protein expression CMC0019 OverExpress C43(DE3) Chemically Competent Cells ≥ 1 × 106 F – ompT hsdSB (rB- mB-) gal dcm (DE3) N
for the highest protein expression CMC0020 OverExpress C43(DE3) pLysS Chemically Competent Cells ≥ 1 × 106 F – ompT hsdSB (rB- mB-) gal dcm (DE3) pLysS (CmR) N
for the highest protein expression CMC0021 OverExpress C41(DE3) Electrocompetent Cells
≥ 1 × 1010 F – ompT hsdSB (rB- mB-) gal dcm (DE3) N
for the highest protein expression CMC0022 OverExpress C43(DE3) Electrocompetent Cells ≥ 1 × 1010 F – ompT hsdSB (rB- mB-) gal dcm (DE3) N
for controlled protein expression CMC0023 CONTROLLER SIG10 Chemically Competent Cells > 1 × 109 mcrA Δ(mrr-hsdRMS-mcrBC) endA1 recA1 ɸ80dlacZΔM15 ΔlacX74 araD139 Δ (ara,leu)7697 galU galK rpsL (StrR) nupG λ− tonA Mini-F lacIq1 (GentR) N
for controlled protein expression CMC0024 CONTROLLER BL21(DE3) Chemically Competent Cells > 1 × 107 F- ompT hsdSB (rB- mB-) gal dcm (DE3) Mini-F lacIq1(GentR) N


Key to Genotypes

Genotype Description
hsdR17 Mutation that inhibits microbe sensing presence of foreign DNA
F’ episome Self-transmissible, low copy number plasmid used to generate ssDNA when infrected with M13 bacteriophage
D(lacZ)M15 Allows for blue/white screening
ton A Resistance to bacteriophages T1, T5 and f80
ompT- Lacking outer membrane protease, which reduces degredation and improves protein recovery
pLysS Encodes the T7 lysozyme; used to reduce basal expression by inhibiting RNA polymerase
CmR Resistance to chloramphenicol
endA1- Mutation in Endonuclease I, eliminating non-specific activity, improving plasmid preps
T1R Resistance to T1 bacteriophage
recA1-
DNA recombination gene mutation – useful for cloning genes with direct repeats