A bacterial inducible operon, similar to the lac operon, contains three genes—R, T, and S—that are involved in coordinated regulation of transcription. One of these genes is an operator region, one is a regulatory protein, and the third produces a structural enzyme. In the table below, '+' indicates that the structural enzyme is synthesized and '−' indicates that it is not produced. Use the information provided to determine which gene is the operator, which produces the regulatory protein, and which produces the enzyme.

Genotype                          Enzyme Synthesis
                             Inducer Present      Inducer Absent
R⁺S⁺T⁺                               +                          –
R⁻S⁺T⁺                                –                          –
R⁺S⁻T⁺                                +                          +
R⁺S⁻T⁺                                +                          +
R⁻S⁺T⁺/R⁺S⁻T⁻                      +                          +
R⁺S⁻T⁺/R⁻S⁺T⁻                      +                          +
R⁺S⁺T⁻/R⁻S⁻T⁺                      +                          –

Key Concepts

Operon Structure

An operon is a cluster of genes under the control of a single promoter, allowing coordinated regulation of gene expression. In bacterial systems, operons typically consist of structural genes that encode proteins, a promoter where RNA polymerase binds, and an operator that acts as a regulatory switch. Understanding the operon structure is crucial for analyzing how genes are turned on or off in response to environmental signals.

Regulatory Proteins

Regulatory proteins are molecules that bind to specific DNA sequences, such as operators, to control the transcription of genes. In the context of an inducible operon, these proteins can act as repressors or activators, determining whether the structural genes are expressed based on the presence or absence of an inducer. Recognizing the role of regulatory proteins is essential for understanding gene regulation mechanisms.

Inducible Systems

Inducible systems are genetic regulatory mechanisms that allow the expression of genes in response to specific signals, such as the presence of an inducer. In the case of the lac operon, for example, the presence of lactose induces the expression of genes necessary for its metabolism. This concept is vital for interpreting the data provided in the question, as it helps explain how the presence or absence of inducers affects enzyme synthesis.