The BL21(DE3) Competent Cells are designed for high-level protein expression and easy induction using T7 promoter constructs. These strains are lysogens of bacteriophage DE3, a lambda derivative containing the gene for T7 RNA polymerase under control of the lacUV5 promoter. Induction with IPTG allows production of T7 RNA Polymerase which then directs the expression of the target gene located downstream of the T7 promoter in the expression vector. Each BL21 (DE3) strain provides varying degrees of regulation and expression control. Recombinant proteins that are non-toxic to E. coli are generally expressed at higher levels in BL21 (DE3) cells than in BL21 (DE3) pLysS or BL21 (DE3) pLysE. Efficiency: >1 x 10e7cfu/ug
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