- Escherichia coli (E. coli) BL21(DE3)pLysS is a widely used strain for controlled recombinant protein expression, particularly when working with proteins that are toxic, unstable, or prone to premature expression.
- This strain is a derivative of E. coli BL21(DE3), which contains the λDE3 lysogen encoding T7 RNA polymerase under the control of the lacUV5 promoter.
- In the presence of an inducer such as IPTG, T7 RNA polymerase is produced, driving high-level expression of target genes cloned under a T7 promoter.
- What distinguishes BL21(DE3)pLysS from BL21(DE3) is the presence of a plasmid (pLysS) that expresses T7 lysozyme, a natural inhibitor of T7 RNA polymerase. T7 lysozyme partially suppresses basal (leaky) expression of the target gene before induction. This is especially beneficial when expressing proteins that are toxic or otherwise detrimental to the host cells if produced constitutively or at high levels without tight control. The strain also carries resistance to chloramphenicol, which is used to maintain the pLysS plasmid.
- While the addition of T7 lysozyme reduces background expression and improves cell viability before induction, it can also slightly lower the overall yield of protein after induction compared to BL21(DE3). Therefore, this strain is typically chosen when the tight regulation of gene expression is more important than absolute yield.
- In summary, E. coli BL21(DE3)pLysS offers a valuable balance between control and efficiency in recombinant protein expression, particularly for sensitive or toxic targets.
