- T7 lysozyme is a bacteriophage-encoded protein that serves a dual role: it functions both as a lytic enzyme during the phage life cycle and as a natural inhibitor of T7 RNA polymerase.
- In molecular biology, its inhibitory function is particularly valuable in expression systems that utilize the T7 promoter.
- T7 lysozyme binds directly to T7 RNA polymerase, inhibiting its activity and thereby reducing basal or leaky expression of target genes prior to induction with IPTG. This is especially important when working with toxic, unstable, or aggregation-prone proteins, where even low levels of unintended expression can negatively impact host cell growth or protein quality.
- To take advantage of this property, engineered E. coli strains such as BL21(DE3)pLysS and pLysE carry a plasmid encoding T7 lysozyme under a constitutive promoter.
- The “pLysS” version expresses the lysozyme at low levels, providing mild repression and making it suitable for most applications, while “pLysE” provides higher levels of T7 lysozyme and is used for more stringent suppression.
- Upon IPTG induction, T7 RNA polymerase is produced in excess, overwhelming the inhibition and enabling robust transcription from the T7 promoter. This balancing act between repression and induction makes T7 lysozyme a critical regulatory tool in T7-based expression systems, improving stability and reproducibility in the production of recombinant proteins.
