Description: BL21 Competent Cells are used for high-level expression of proteins from vectors containing E. coli promoters such as trc, tac, λPL, and araD. T7 RNA Polymerase expression in BL21(DE3) cells permits IPTG induction of protein expression. Addition of the pLysS or pLysE plasmid provides tighter promoter control when expressing proteins toxic to the cells. Genotypes: BL21 F– ompT hsdSB(rB–mB–) gal dcm BL21(DE3) F–, ompT, hsdSB (rB–mB–), dcm, gal, λ (DE3) BL21(DE3)pLysE F– ompT hsdSB (rB–mB–) gal dcm (DE3)pLysE (CamR ) BL21(DE3)pLysS F– ompT hsdSB (rB–mB–) gal dcm (DE3)pLysS (CamR ) Storage: Store at -80°C. Shipping method: Protein Expression Competent Cells are packaged with dry ice and shipped overnight.