And this repressor gene is also part of this opera. That repressor gene basically codes for an inactive so, not an active repressor protein. And to activate that inactive repressor protein so that it can bind onto the operator segment, a special thing must happen. Tryptophan must bind onto the inactive form of that repressive protein to activate it. And only then will that repressive protein bind onto the operator and inhibit the expression of these genes. And therefore inhibit the expression, the formation of tryptophan.