If a mutation prevents RNA polymerase from binding to the promoter, what is the most likely outcome for transcription?

• A. Transcription would be unaffected.
• B. Translation would increase.
• C. RNA polymerase would bind to alternative sites and start transcription.
• D. Transcription would be greatly reduced or abolished.

Answer: (D)

Transcription starts when RNA polymerase recognizes and binds to the promoter region upstream of a gene. The promoter provides the specific DNA sequence that the polymerase (often with a sigma factor in bacteria) needs to assemble the transcription initiation complex and begin RNA synthesis. If a mutation blocks RNA polymerase from binding the promoter, the initiation complex cannot form, so transcription cannot start. Since transcription is the first step producing the mRNA that will later be translated, no mRNA would be made, and translation would not occur for that gene. While the polymerase might bind non‑specifically to other DNA regions, productive transcription relies on promoter recognition, so the overall level of transcription would be greatly reduced or abolished.