Within the realm of E. coli expression, the T7 system is the most popular approach for producing recombinant protein. In this system, the target gene is cloned into an expression vector downstream of the T7 promoter and this construct is introduced into a T7 expression host. NEB offers several T7 system strains of competent E. coli for protein expression.
- BL21(DE3) Competent E. coli (NEB #C2527), are chemically competent E. coli cells suitable for transformation and routine protein expression. This strain expresses the T7 RNA polymerase and is deficient in proteases Lon and OmpT. These cells are extremely pure and free of animal products.
- Lemo21(DE3) Competent E. coli (NEB #C2528) is a BL21(DE3) strain containing the Lemo System™, offering tunable expression of difficult clones. Tunable expression is achieved by varying the level of lysozyme (lysY), the natural inhibitor of T7 RNA polymerase. The level of lysozyme is modulated by adding L-rhamnose to the expression culture at levels from zero to 2000 µM. When Lemo21(DE3) is grown without rhamnose, the strain performs the same as a pLysS containing strain. However, optional addition of rhamnose tunes the expression of the protein of interest. For difficult soluble proteins, tuning the expression level may also result in more soluble, properly folded protein.
- NiCo21(DE3) Competent E. coli (NEB #C2529) are chemically competent E. coli cells derived from BL21(DE3). Poly-histidine tagged recombinant proteins that are isolated by immobilized metal affinity chromatography (IMAC) are often contaminated with significant amounts of endogenous E. coli metal binding proteins. The protein expression strain NiCo21(DE3) has been engineered to minimize E. coli protein contamination of IMAC fractions: endogenous GlmS is mutated to eliminate binding to IMAC resins and three other proteins (SlyD, ArnA and Can) are tagged to enable rapid removal by chitin affinity chromatography.
- The T7 Express High Efficiency Group of Competent Cells includes three different strains, including T7 Express lysY/Iq Competent E. coli (High Efficiency) (NEB #C3013), T7 Express lysY Competent E. coli (High Efficiency) (NEB #C3010) and T7 Express Competent E. coli (High Efficiency) (NEB #C2566).
- What are the strain properties (C2566)?
- Is T7 Express (NEB #C2566H and NEB #C2566I) compatible with auto-induction procedures?
- What are the strain properties (C2527)?
- What is the difference between T7 Express (NEB #C2566H/I) and BL21(DE3) (NEB #C2527H/I)?
- Can the NEBExpress Competent E.coli (High Efficiency) be used for the expression of constructs containing a T7 promoter?
Avoid Common Obstacles in Protein Expression
Read how to avoid common obstacles in protein expression that prevent interactions with cellular machinery.
- Competent Cell Brochure
- Protein Expression & Purification Brochure
- Competent Cell Product Comparison
- Competent Cell Selection Guide
E. coli Hosts
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