One Shot® BL21(DE3) Chemically Competent E. coli are ideal for use with bacteriophage T7 promoter-based expression systems (e.g., pRSET, pCR™T7, and pET). BL21(DE3) cells carry the lambda DE3 lysogen. Recombinant proteins that are nontoxic to E. coli are generally expressed at higher levels in BL21(DE3) cells than in BL21(DE3)pLysS or BL21(DE3)pLysE. However, the basal expression levels of heterologous genes are significantly higher in BL21(DE3) than in BL21(DE3)pLysS or BL21(DE3)pLysE.
About BL21 strains BL21 strains are descended from the E. coli B strain and have been specifically constructed for high-level expression of recombinant proteins. These strains have two important attributes that make them ideal for protein expression: key genetic markers and inducibility of protein expression. The most important genetic markers help recombinant RNA and/or protein accumulate to high levels without degradation. Inducibility helps to minimize the toxic effects of some recombinant proteins.
For Research Use Only. Not for use in diagnostic procedures.
Bacterial or Yeast Strain
Cloning Methylated DNA
Competent Cell Type
F'episome (to make ssDNA)
Lacks F' Episome
Not High-throughput Compatible (Manual)
Propagating ccdB Vectors
Not for ccdB vector propagation
T1 Phage - Resistant (tonA)
Transformation Efficiency Level
Medium Efficiency (10^8-10^9 cfu⁄µg)
20 x 50 µL
Improves Plasmid Quality
Contents & Storage
Contains: • One Shot™ BL21(DE3) E.coli: 20 vials, 50 µl each (total of 1 ml) • pUC19 DNA (10 pg/ul): 1 vial, 50 µl • SOC Medium: 1 bottle, 6 ml
Store Competent Cells at -80°C. Store pUC19 DNA at -20°C. Store SOC Medium at 4°C or at room temperature.