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.

rhaPBAD promoter

Variable from low to high level
(L-rhamnose)

Tight regulation. Low basal activity. Relatively expensive inducer.