Lucigen’s E. cloni EXPRESS BL21(DE3) Electrocompetent Cells are the first to offer high efficiency cloning and high level protein expression in the same cell. Cloning efficiencies are increased 25-1,000 fold relative to competitors’ preparations of BL21 cells (Figure 1), which is essential for construction of complex expression libraries. The unprecedented transformation efficiency of E. cloni EXPRESS Electrocompetent Cells (> 5 × 10⁹ cfu/µg) eliminates the need for plasmid transfer from the cloning strain to the expression strain, saving days of work in a typical cloning and expression experiment (Figure 2)

Figure 1. Transformation efficiency comparison of commercially available BL21(DE3) competent cells.

E. cloni EXPRESS BL21(DE3) strains contain the phage T7 RNA polymerase gene linked to the IPTG-inducible promoter, for use with any expression plasmid containing the T7 promoter.

EXPRESS pLysS Electrocompetent Cells (> 2 × 10⁸ cfu/µg) also produce T7 lysozyme to repress low-level transcription from the T7 promoter prior to IPTG induction, helping to stabilize inserts coding for deleterious products. EXPRESS pLysE Electrocompetent Cells > 2 × 10⁸ cfu/µg) have a higher level of repression by T7 lysozyme, offering the greatest control over expression of inserts. The ComboPack™ contains 4 transformations each of the E. cloniEXPRESS Competent Cell strains, to determine which works best in expressing your protein of interest.

NOTE: For best results in expressing proteins that may be toxic, we recommend using OverExpress Cells instead of EXPRESS pLysS or pLysE strains. All three E. cloni EXPRESS strains are also available as chemically competent cells. With a transformation efficiency of >1 × 10⁷ cfu/µg and very economical prices, EXPRESS Chemically Competent Cells offer superior value for everyday protein expression work.