You are investigating a new bacterial operon that contains five regions (A, B, C

Question

You are investigating a new bacterial operon that contains five regions (A, B, C, D and E) involved in coordinated regulation of transcription. One is the gene for a regulatory protein, one is the binding site for the regulatory protein, two produce structural enzymes (enzyme 1 and enzyme 2), and one is the promoter for the two enzyme genes.

The table below shows data collected for five different bacterial strains. A "+" indicates that the structural enzyme is produced and a "-" indicates that the enzyme is not produced. The "signal" is a molecule that either represses or induces the operon. Use the information to determine how the operon is regulated, and the identity of each region.

Part B

Parts of an operon that control the expression of both enzyme genes are called "regulatory regions." The genes that produce the enzymes are called "structural genes." Using the data in the table, determine which regions are regulatory regions and which are structural genes.

Sort each region into the correct category.

Regions: A, B, C, D, E

Regulatory Region(s) Structural Gene(s)

Strain Enzyme 1 Enzyme 1 Enzyme 2 Enzyme 2 -signal +signal -signal +signal A+B+C+D+E+ + - + - A-B+C+D+E+ - - - - A+B-C+D+E+ + + + + A+B+C-D+E+ + - - - A+B+C+D-E+ + + + + A+B+C+D+E- - - + -

Explanation / Answer

Part A :

Strain 1 : Presence of inducer binds to the regulator protein, hence the repressors cannot bind to the operator i.e. the binding site for regulatory protein. So, the enzymes are produced in presence of inducer whereas, in its absence the repressor binds to the operator and inhibit the enzyme production.

Strain 2: Promoter (A-) is mutated, so RNA polymerase cannot bind to it, hence no transciption occurs,resulting in no enzyme formation.

Strain 3: Mutation in regulatory protein (B-), so there is no repressor. Hence, constitutive expression of enzymes, in presence or absence of signal.

Strain 4: Gene for production of structural enzyme 2 is mutated (C-), therefore, no production of enzyme 2 in presence or absence of signal.

Strain 5: Operator is mutated (D-), so repressor cannot bind to it, hence constitutive synthesis of both enzymes found.

Strain 6: Gene for production of structural enzyme 1 is mutated (E-), therefore, no production of enzyme 1 in presence or absence of signal.

Part B:

Regulator Protein: B

Binding site for regulator protein : D

Promoter: A

Structural genes : E (for enzyme 1), C (for enzyme 2)

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