| Criteria | pLysS System | pLysE System | Remarks |
| Encoded Protein | T7 Lysozyme (low expression level) | T7 Lysozyme (high expression level) | Both express T7 lysozyme to inhibit T7 RNA polymerase. |
| Plasmid Copy Number | Low to moderate | Higher than pLysS | Affects the amount of T7 lysozyme produced. |
| T7 Lysozyme Level | Moderate | Elevated | pLysE leads to stronger inhibition of T7 RNA polymerase. |
| Inhibition of T7 RNA Polymerase | Partial inhibition – reduces leaky expression | Strong inhibition – tighter suppression | pLysE provides stricter control over basal expression. |
| Suitability for Toxic Protein Expression | ✅ Suitable for moderately toxic proteins | ✅✅ Best suited for highly toxic or membrane-disrupting proteins | pLysE offers tighter regulation, preventing premature toxicity. |
| Expression After Induction | High expression levels possible post-IPTG induction | Slightly reduced yield due to higher initial inhibition | pLysE may lower final yield slightly but offers greater control. |
| Background Expression (Leakiness) | Moderate suppression of background (basal) expression | Strong suppression, nearly complete | pLysE is better for sensitive expression systems. |
| Antibiotic Selection Marker | Chloramphenicol resistance | Chloramphenicol resistance | Identical resistance; distinguish by plasmid origin and behavior. |
| Origin of Replication | pACYC-based (low-copy number) | pACYC-based (low-copy number) | Backbone is similar; difference lies in lysozyme expression control. |
| Inducibility & Compatibility | Compatible with pET/T7 systems; induced with IPTG in DE3 strains | Same as pLysS | Both systems require DE3 strains (e.g., BL21(DE3)) for functional use. |
| Use in Common Strains | BL21(DE3)pLysS, C41(DE3)pLysS | BL21(DE3)pLysE, C41(DE3)pLysE | Choice depends on desired regulation tightness. |
| Plasmid Burden on Host | Lower | Slightly higher | pLysE may slow growth slightly due to increased lysozyme load. |
