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Single Step (KRX) Competent Cells

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Ready-to-Transform E. coli Strain with Tightly Controlled Protein Expression

  • Ready for protein expression two days after transformation
  • Dramatic control of expressed protein-coding regions with higher protein yields than BL21(DE3)-derived strains
  • Convenient blue/white screening for detecting recombinant clones


Catalog number selected: L3002

$ 380.00
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Single Step (KRX) Competent Cells
20 × 50μl
$ 380.00
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Competent Cells for Efficient, Controlled Protein Expression

The Single Step (KRX) Competent Cells are designed for efficient transformation and tightly controlled protein expression. These cells consolidate the best attributes of these two steps into one strain to evaluate protein expression in E. coli. In two days, you can transform your vector into the Single Step (KRX) Competent Cells and be ready for protein expression. Transformation efficiencies are greater than 108 cfu/μg, similar to other highly competent cells. The single step cells are available in single transformation size (50μl). KRX also can be used for blue/white screening. Single Step (KRX) is an E. coli K strain that contains a chromosomal copy of the T7 RNA polymerase driven by a rhamnose promoter (rhaBAD) to provide dramatic control of the proteins expressed via a T7 promoter. Pre-induced expression protein levels are significantly lower than those of BL21(DE3)-derived strains. This feature facilitates cloning and expression of proteins toxic to E. coli.

Genotype: [F´, traD36, ΔompP, proA+B+, lacIq, Δ(lacZ)M15] ΔompT, endA1, recA1, gyrA96 (Nalr), thi-1, hsdR17 (rk, mk+), e14 (McrA), relA1, supE44, Δ(lac-proAB), Δ(rhaBAD)::T7 RNA polymerase.

Comparison of protein overexpression.

Comparison of protein overexpression. Lane 1, BL21(DE3); lane 2, BL21(DE3)pLysS; lane 3, Rosetta 2(DE3) pLysS; lane 4, Single Step (KRX) Competent Cells.


What's in the box?

Item Part # Size

Single Step (KRX) Competent Cells

L300B 20 × 50μl

Certificate of Analysis

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Use Restrictions

For Research Use Only. Not for Use in Diagnostic Procedures.

Storage Conditions


See Protocol for storage recommendations.

Patents and Disclaimers

U.S. Pat. No. 9,469,857, European Pat. No. 1847611 and Japanese Pat. No. 5456706.

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