So usually we have a low intracellular concentration of tryptophan. So inside the cell we have a relatively low amount of tryptophan. Now what exactly will that mean? Well, if we have a low amount of tryptophan inside the cell then our inactive repressive protein will remain inactive because there isn't enough tryptophan to actually bind onto the allosteric side of this inactive repressive protein to activate it. So usually what happens is this gene is expressed to produce the repressor mRNA and then that mRNA is used to form the inactive repressor protein. And because we don't have enough we don't have a lot of tryptophan in our cell.