trc (trp-lac) promoter

The trc promoter is a hybrid of the lac and trp promoters which is a stronger promoter in comparison to the lac promoter. The trc promoter was created by insertion of 1 bp into the 16 bp sequence between the consensus -35 and -10 sequences of the tac promoter, to obtain the optimal consensus distance of 17 bp between the -35 and -10 signal. This promoter includes the lac operator sequence lacO, which can be bound by the Lac repressor lacI. For inducible gene expression from the trc promoter the lac repressor (LacI) is necessary. The repressor binds to the operator DNA with high specificity and inhibits gene expression until an inducer like allolactose or the analog IPTG (Isopropyl-?-D-thio-galactoside) is added to the medium. The inducer binds to the repressor, causing a change in its shape. Thus altered, the repressor is unable to bind to the operator, allowing RNA polymerase (RNAP) to transcribe the following genes and thereby leading to high levels of the encoded proteins.