Product Class: Competent Cell

NEB Express Competent E. coli (High Efficiency)

NEB does not add a dry ice surcharge to our competent cell shipments.
Catalog #SizeConcentration
C2523I6 x 0.2 ml/tube
C2523H20 x 0.05 ml/tube



  • Transformation efficiency: 0.6-1 x 109 cfu/μg pUC19 DNA
  • Enhanced BL21 derivative ideal for Plac, Ptac, Ptrc expression vectors
  • Deficient in proteases Lon and OmpT
  • Resistant to phage T1 (fhuA2)
  • Does not restrict methylated DNA (McrA-, McrBC-, EcoBr-m-, Mrr-)
  • Free of animal products


  • Versatile non-T7 expression strain
  • Protease deficient


fhuA2 [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


Chemically competent E. coli cells suitable for high efficiency transformation and protein expression. Recommended host strain for pMAL Protein Fusion and Purification System.
DNA Effects on Transformation Efficiency and Colony Output: The optimal amount of DNA to use in a transformation reaction is lower than commonly recognized. Using clean, supercoiled pUC19, the efficiency of transformation is highest in the 100 pg-1 ng range. However, the total colonies which can be obtained from a single transformation reaction increase up to about 100 ng.
Effect of heat shock time on NEB 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 NEB 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
Tetracycline15 μg/ml
Streptomycin25 μg/ml

Storage Temperature


Shipping Notes

  • Ships on dry ice

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.

Supporting Documents

The following is a list of Safety Data Sheet (SDS) that apply to this product to help you use it safely.
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 or fill out the Technical Support Form for appropriate document.


  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.
  1. Does New England Biolabs offer strains of Competent E.coli suited for protein expression?
  2. How long should I incubate cells on ice after DNA has been added (NEB #C2523H and NEB #C2523I)?
  3. What are the solutions/recipes (C2523)?
  4. What are the strain properties (C2523)?
  5. What is the difference between NEB #C2523H and NEB #C2523I?
  6. Why are there no colonies or no growth in liquid culture (C2523)?
  7. Why is induced protein insoluble (C2523)?
  8. Why is there no protein visible on gel or no activity (C2523)?
  9. Can I store competent cells at -20°C instead of -80°C?
  10. Can the NEB Express Competent E.coli (High Efficiency) be used for the expression of constructs containing a T7 promoter?
  11. What is the optimal heat shock time for this strain (NEB #C2523H and NEB #C2523I)?
  12. Which kind of transformation tubes should be used?
  13. What volume of DNA can be added into competent cells?
  14. What is the shelf life for this strain (NEB #C2523H and NEB #C2323I)?
  15. Are NEB's competent cells compatible with the "Plate and Go" protocol?
  1. High Efficiency Transformation (C2523)
  2. 5 Minute Transformation (C2523)
  3. Expression Using NEB Express (C2523)

Application Notes