IPTG and lac operator with e coli for foreign gene question We did an experiment were we have e coli with a plasmid with a gene from another bacteria in it, and we put in IPTG in for induction. Will after looking up more about IPTG online I see it's related to the lac operator, which from what I've found just deals with lactose. Is there some other function that has? How can this be related to or effect the thing we put in and what we're doing? I'm missing the connection here.

The lac operon contains genes which are important for the metabolization of lactose as an energy source - normally glucose is used for this purpose. Usually the operon is tighly regulated and as long as there is another source of energy it is kept in an inhibited state.

The presence of lactose removes the lac repressor from the lac operon and allows the expression of the genes and thus allowing the metabolization of lactose. The mechanism can be turned on and off depending on the presence of lactose.

IPTG is a substance which mimicks the presence of allolactose (a metabolite of lactose) and it can activate transcription from the lac operon. As IPTG (in contrast to allolactose) cannot be hydrolyzed by β-galactosidase, it's concentration in the cell stays the same. Using the lac operon and IPTG enables you to switch on the expression of the gene on your plasmid and to start the overexpression.