The prokaryotic core RNA polymerase combines with which factor to form the RNA polymerase holoenzyme?

The prokaryotic core RNA polymerase combines with which factor to form the RNA polymerase holoenzyme?

• A. Alpha subunit
• B. Beta subunit
• C. Omega subunit
• D. Sigma factor

Answer: (D)

In bacteria, transcription initiation requires the holoenzyme, which forms when the core RNA polymerase associates with a sigma factor. The sigma factor provides promoter recognition—it binds to specific DNA sequences at the promoter and guides the enzyme to the correct start site. This partnership makes initiation precise; without sigma, the core enzyme can still synthesize RNA but does so with little promoter specificity. The other subunits mainly contribute to the core’s catalytic activity and structural assembly, not promoter targeting. Once initiation begins, the sigma factor often dissociates, allowing the core enzyme to proceed into elongation.

In bacteria, transcription initiation requires the holoenzyme, which forms when the core RNA polymerase associates with a sigma factor. The sigma factor provides promoter recognition—it binds to specific DNA sequences at the promoter and guides the enzyme to the correct start site. This partnership makes initiation precise; without sigma, the core enzyme can still synthesize RNA but does so with little promoter specificity. The other subunits mainly contribute to the core’s catalytic activity and structural assembly, not promoter targeting. Once initiation begins, the sigma factor often dissociates, allowing the core enzyme to proceed into elongation.