Which of the following is NOT a component of the core enzyme for bacterial RNA polymerase?

The correct answer indicates that the σ subunit is not a component of the core enzyme of bacterial RNA polymerase. The core enzyme is composed of the α2, β, and β′ subunits. This structure is essential for the RNA polymerase's ability to synthesize RNA from a DNA template.

The σ factor, while essential for the initiation of transcription, is not included in the core enzyme itself. Instead, it is a separate protein that associates with the core enzyme to form the holoenzyme, which is responsible for recognizing the promoter regions on DNA and initiating transcription. This distinction is key, as the core enzyme is involved in elongation and does not include the σ subunit, which plays a crucial role only early in the transcription process.

In summary, understanding the components of the core enzyme and the separate function of the σ factor clarifies why the σ subunit is not classified as part of the core enzyme of bacterial RNA polymerase.