Abacterial operon is responsible for the production of the biosynthetic enzymes needed to make the hypothetical amino acid tisophane (tis). the operon is regulated by a separate gene, r. the deletion of r causes the loss of enzyme synthesis. in the wild-type condition, when tis is present, no enzymes are made; in the absence of tis, the enzymes are made. mutations in the operator gene (o−) result in repression regardless of the presence of tis.