Question

A bacterial 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 wildtype condition, when tis is present, no enzymes are made; in the absence of tis, the enzymes are made. Mutations in the operator gene $\left(O^{-}\right)$ result in repression regardless of the presence of tis. Is the operon under positive or negative control? Propose a model for (a) repression of the genes in the presence of tis in wild-type cells and (b) the mutations.

          A bacterial 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 wildtype condition, when tis is present, no enzymes are made; in the absence of tis, the enzymes are made. Mutations in the operator gene $\left(O^{-}\right)$ result in repression regardless of the presence of tis. Is the operon under positive or negative control? Propose a model for (a) repression of the genes in the presence of tis in wild-type cells and (b) the mutations.

Added by Lawrence S.

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