Cited in over 350 research articles, Lucigen’s OverExpress C41(DE3) and C43(DE3) Competent Cells are highly effective in expressing toxic and membrane proteins

With these BL21(DE3) derivatives, you can efficiently and reliably express genes cloned into any T7 vector. E. coli BL21(DE3) strains, like Lucigen’s E. cloni EXPRESS Competent Cells, provide reliable expression of many genes cloned into T7 expression vectors (e.g., pET or Lucigen's Expresso T7 vectors). However, in some cases expression is minimal or undetectable because the recombinant protein, when expressed, is deleterious or lethal to these standard BL21 strains. Examples of such toxic proteins include many membrane proteins, some cytoplasmic proteins, and nucleases. Unfortunately, successful expression of one or more toxic proteins is often very important to the experimental goal. Lucigen’s OverExpress Electrocompetent and Chemically Competent Cells are E. coli strains that are effective in expressing toxic proteins from all classes of organisms. These include toxic proteins from eubacteria, yeasts, plants, viruses, and mammals.

The OverExpress strains contain genetic mutations phenotypically selected for conferring tolerance to toxic proteins. The strain C41(DE3) was derived from BL21(DE3). This strain has at least one mutation, which prevents cell death associated with expression of many recombinant toxic proteins. The strain C43(DE3) was derived from C41(DE3) by selecting for resistance to a different toxic protein and can express a different set of toxic proteins to C41(DE3).

As in standard BL21(DE3) strains, OverExpress C41(DE3), C41(DE3)pLysS, C43(DE3), and C43 (DE3)pLysS are lysogens of λDE3. These strains carry a chromosomal copy of the T7 RNA Polymerase gene under the control of the lacUV5 promoter. These strains are suitable for production of protein from target genes cloned into T7-driven expression vectors. OverExpress C41(DE3), C41(DE3) pLysS, C43(DE3), and C43(DE3) pLysS are also deficient in the lon and ompT proteases. OverExpress C41(DE3)pLysS and C43(DE3)pLysS also carry a chloramphenicol-resistant plasmid that encodes T7 lysozyme, which is a natural inhibitor of T7 RNA polymerase. Cells containing pLysS produce a small amount of T7 lysozyme. These strains are used to suppress basal expression of T7 RNA polymerase prior to induction, thus stabilizing recombinants encoding particularly toxic proteins.

Which Lucigen OverExpress Competent Cell strain is ideal for your purposes?: It is difficult to predict which of the four OverExpress strains – C41(DE3), C43(DE3), C41(DE3)pLysS, or C43(DE3)pLysS – will work best in expressing a given protein. We recommend initially using the OverExpress ComboPack which contains 3 reactions each of the four OverExpress competent cell strains, to determine which one is best for your application. The OverExpress strains are available as electrocompetent or chemically competent cells.

Important Product Use Information: OverExpress Cells are licensed exclusively to Lucigen Corporation by Imaxio S.A. under US Pat. 6,361,966 and others. Purchase of OverExpress Cells is accompanied by a non-exclusive, non-transferable license for research use only. Commercial use requires a separate license available from Imaxio S.A. OverExpress Cells are also sold under a license issued to Lucigen Corporation by Brookhaven Science Associates, LLC (BSA) for research use by noncommercial entities. Commercial entities require a license from BSA even for research use.