And a repressible opera is usually on, but sometimes under certain circumstances it can be turned off as we'll see in just a moment. So a tryptophan Operon is an Operon that is used by bacterial cells to basically regulate the synthesis of the tryptophan amino acid. So let's take a look at the different components of the tryptophan opera. So notice that the tryptophan Operon contains the blue section and that is the promoted section. Now the promoted section is important because this is where the RNA polymerase binds to. So when the RNA polymerase approaches the promoter, it binds onto the promoter.