Description
BL21(DE3)pLysE E. coli are ideal for use with T7 promoter-based expression vectors. Like BL21(DE3)pLysS E. coli, BL21(DE3)pLysE carry the lambda DE3 lysogen. In addition, BL21(DE3)pLysE cells contain the pLysE plasmid, which constitutively expresses T7 lysozyme. T7 lysozyme reduces the basal expression of target genes by inhibiting T7 RNA polymerase. The pLysE plasmid in BL21(DE3)pLysE expresses higher levels of T7 lysozyme than the pLysS plasmid in BL21(DE3)pLysS. The BL21(DE3)pLysE strain provides tighter control of T7 RNA polymerase, which is necessary when the recombinant protein to be expressed is toxic.