Promoters
| Overview of E. coli promoter systems useful for heterologous protein production | ||
|---|---|---|
| Promoters | expression Level (inductor) | Key features |
| lac promoter | Low level up to middle (IPTG) | Weak, regulated suitable for gene products at very low intracellular level. Comparatively expensive induction. |
| trc and tac promoter | Moderately high (IPTG) | High-level, but lower than T7 system. Regulated expression still possible. Comparatively expensive induction. High basal level. |
| T7 RNA polymerase | Very high (IPTG) | Utilizes T7 RNA polymerase. High-level inducible over expression. T7lac system for tight control of induction needed for more toxic clones. Quite expensive induction. Basal level depends on strain used (pLys). |
| Phage promoter pL | Moderately high (temperature shift) | Temperature-sensitive host required. Less likelihood of "leaky" un-induced expression. Basal level; high basal level by temperatures below 30°C. No inducer. |
| tetA promoter/operator | Variable from middle to high level (anhydrotetracyclin) | Tight regulation. Independent of metabolic state. Independent of E. coli strain. Relatively inexpensive inducer. Low basal level. |
| PPBAD promoter | Variable from low to high level (L-arabinose) |
Can fine-tune expression levels in a dose-dependent manner. Tight regulation possible. Low basal level. Inexpensive inducer. |
| PBAD promoter | Variable from low to high level | Tight regulation. Low basal activity. Relatively expensive inducer. |
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