| Criteria | BL21(DE3)pLysS | BL21(DE3) CodonPlus | Remarks |
| Genetic Background | Derivative of E. coli BL21(DE3) containing the pLysS plasmid | Derivative of BL21(DE3) engineered to carry additional tRNA genes for rare codons | Both are BL21(DE3) derivatives, commonly used for T7 promoter-driven protein expression. |
| Key Feature | Contains T7 lysozyme, which inhibits basal expression of T7 RNA polymerase | Contains extra copies of tRNA genes (e.g., argU, ileY, leuW) for rare codons | pLysS = tighter control; CodonPlus = improved translation of codon-biased genes. |
| Control of Expression | Tight control of expression, reduces leaky expression of toxic proteins | No extra expression control but improves translation efficiency for codon-rich genes | pLysS is useful when protein toxicity is a concern. |
| Plasmid Present | Yes – pLysS plasmid (chloramphenicol resistant) | Yes – plasmid(s) for tRNA expression (e.g., chloramphenicol or streptomycin resistant) | Antibiotic selection differs and should be considered during co-transformation. |
| Ideal For | Expression of toxic or tightly regulated proteins | Expression of eukaryotic or AT-rich genes with rare codons in E. coli | CodonPlus is preferred for expressing genes from organisms with codon bias different from E. coli. |
| Expression Efficiency | Moderate expression levels due to suppression by T7 lysozyme | Generally higher protein yield for codon-biased genes | CodonPlus improves protein folding and solubility for such genes. |
| Induction System | T7 promoter system induced with IPTG | Same – T7 promoter induced with IPTG | Both use IPTG-inducible systems; control levels differ. |
| Toxic Protein Management | Reduces toxicity by limiting basal expression | No control of basal expression – may cause issues with toxic proteins | Use pLysS for tight regulation when protein is lethal or inhibitory to host growth. |
| Compatibility with Vectors | Compatible with T7-based expression vectors (e.g., pET series) | Same – compatible with T7-based vectors | Both support common T7-based systems. |
| Applications | Toxic protein expression, basic protein expression requiring low background | Heterologous expression of genes with rare codons, including mammalian, parasite, or viral genes | Application choice depends on gene codon usage and protein toxicity. |
