- The T7 promoter is a bacteriophage-derived promoter that is widely used for high-level expression of recombinant proteins in Escherichia coli systems.
- It is recognized exclusively by T7 RNA polymerase, not by the host’s native E. coli RNA polymerase, making it highly specific and capable of driving extremely strong transcription of downstream genes.
- In engineered expression systems, such as the popular pET plasmid series, the T7 promoter is paired with E. coli strains like BL21(DE3), which carry a chromosomal copy of the T7 RNA polymerase gene under the control of an inducible promoter, typically lacUV5.
- Upon induction with IPTG, T7 RNA polymerase is produced and rapidly transcribes the target gene under control of the T7 promoter.
- The strength and specificity of the T7 promoter system enable exceptionally high protein yields, making it ideal for producing large amounts of recombinant proteins for structural studies, biochemical assays, or industrial applications. However, the system can be leaky (i.e., show basal expression even without IPTG), which may pose problems when expressing toxic or aggregation-prone proteins.
- To mitigate this, modified strains such as BL21(DE3)pLysS or regulatory elements like T7 lysozyme are often used to suppress unintended expression.
- Despite such considerations, the T7 promoter remains a cornerstone of bacterial expression systems due to its powerful performance, tight regulation, and compatibility with a wide array of vectors and host strains.
