• My NEB
  • Print
  • PDF
  • T7 Express Competent E. coli (High Efficiency)


    Chemically competent E. coli cells suitable for high efficiency transformation and protein expression.


    • Transformation efficiency: 0.6-1 x 109 cfu/μg pUC19
    • Enhanced BL21 derivative
    • T7 RNA Polymerase in the lac operon - no λ prophage
    • Deficient in proteases Lon and OmpT
    • Resistant to phage T1 (fhuA2)
    • Does not restrict methylated DNA (McrA-, McrBC-, EcoBr-m-, Mrr-)
    • B Strain
    • Free of animal products


    fhuA2 lacZ::T7 gene1 [lon] ompT gal sulA11 R(mcr-73::miniTn10--TetS)2 [dcm] R(zgb-210::Tn10--TetS) endA1 Δ(mcrC-mrr)114::IS10

    Reagents Supplied

    The following reagents are supplied with this product:

    Store at (°C)Concentration
    pUC19 Transformation Control Plasmid-200.05 ng/μl
    SOC Outgrowth Medium41X

    Advantages and Features


    • Most popular T7 expression strain
    • Protease deficient


    Transformation of a toxic mammalian clone into E. coli hosts. A T7 expression plasmid and the same plasmid containing a gene encoding a toxic mammalian protein were transformed into each host. Comparison of the relative transformation efficiencies demonstrates that the T7 Express hosts provide the levels of control necessary for transformation of potentially toxic clones. BL21(DE3) could not be transformed with the toxic clone.
    T7-controlled expression of a non-toxic protein in E. coli hosts. A T7 expression plasmid containing a gene encoding an E. coli protein was transformed into each host, grown to 0.6 OD and induced for 3 hours. Comparison of soluble extracts from uninduced (-) and induced (+) cells shows superior control of basal expression in the T7 Express hosts while maintaining high levels of induced expression.
    Effect of heat shock time on T7 Express competent E. coli transformation efficiency: 50 μl of competent cells were transformed with 100 pg of pUC19 control DNA following the provided High Efficiency Transformation Protocol except heat shock time varied from 0 to 80 seconds..
    Effect of DNA incubation time on T7 Express competent E. coli transformation efficiency: 50 μl of competent cells were transformed with 100 pg of pUC19 control DNA following the provided High Efficiency Transformation Protocol except DNA incubation time varied from 0 to 40 minutes.

    Properties and Usage

    Antibiotics for Plasmid SelectionWorking Concentration
    Ampicillin100 μg/ml
    Carbenicillin100 μg/ml
    Chloramphenicol33 μg/ml
    Kanamycin30 μg/ml
    Streptomycin25 μg/ml
    Tetracycline15 μg/ml

    Storage Temperature


    Shipping Notes

    • Ships on dry ice

    Antibiotic Resistance

    • nit

    Quality Control

    Quality Control Assays

    The following Quality Control Tests are performed on each new lot and meet the specifications designated for the product. Individual lot data can be found on the Product Summary Sheet/Datacard or Manual which can be found in the Supporting Documents section of this page.
    • Transformation Efficiency:
      The competent cells are tested for transformation efficiency and pass minimum release criteria. Transformation efficiency is defined as the number of colony forming units (cfu) which would be produced by transforming 1 μg of plasmid into a given volume of competent cells.


    1. CAUTION: This product contains DMSO, a hazardous material. Review the MSDS before handling.
    2. STORAGE AND HANDLING: Competent cells should be stored at -80°C. Storage at -20°C will result in a significant decrease in transformation efficiency. Cells lose efficiency whenever they are warmed above -80°C, even if they do not thaw.

    Supporting Documents

    Material Safety Datasheets

    The following is a list of Material Safety Data Sheets (MSDS) that apply to this product to help you use it safely. The following file naming structure is used to name these document files: [Product Name] MSDS. For international versions please contact us at info@neb.com.


    The Product Summary Sheet, or Data Card, includes details for how to use the product, as well as details of its formulation and quality controls. The following file naming structure is used to name the majority of these document files: [Catalog Number]Datasheet-Lot[Lot Number]. For those product lots not listed below, please contact NEB at info@neb.com or fill out the Technical Support Form for appropriate document.
    1. What are the solutions/recipes (C2566)?
    2. What are the strain properties (C2566)?
    3. Why are there no colonies or no growth in liquid culture (C2566)?
    4. Why is there no protein visible on gel or no activity (C2566)?
    5. Why is induced protein insoluble (C2566)?
    6. Can I store competent cells at -20°C instead of -80°C?
    7. What is the difference between NEB #C2566H and NEB #C2566I?
    8. What is the optimal heat shock time for this strain (NEB #C2566H and NEB #C2566I)?
    9. How long should I incubate cells on ice after DNA has been added (NEB #C2566H and NEB #C2566I)?
    10. Is T7 Express (NEB #C2566H and NEB #C2566I) compatible with auto-induction procedures?
    11. Which kind of transformation tubes should be used?
    12. What volume of DNA can be added into competent cells?
    13. What is the shelf life for this strain (NEB #C2566H and NEB #C2566I)?
    14. Are NEB's competent cells compatible with the "Plate and Go" protocol?
    1. High Efficiency Transformation Protocol (C2566)
    2. 5 Minute Transformation Protocol (C2566)
    3. Protocol for Expression Using T7 Express (C2566)

    Selection Tools

    Usage Guidelines & Tips

    Application Notes