Dear Community,
The pET-17b vetctor (the enclosed file) lacks the lac repressor expressing gene, and also seems to lack a lac operator in the upstream of the insert site. However, a lot of literature used pET-17b to express protein with IPTG induction. I am wondering how pET17b could be induced or enhanced for protein expression in this way.
It is because the T7 promoter requires T7 polymerase to function (and not the normal E. coli polymerase). In the expression strains used for pET type plasmids such as BL21 (DE3) and similar, the gene for T7 polymerase is integrated in the host genome and expression of that gene is under control by a lac operator. So the addition of IPTG turns on expression of T7 polymerase and this in turn activates transcription from the T7 promoter of pET17 and other similar vectors.
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