What is a promoter in DNA?

• A. A sequence that signals termination
• B. A sequence where ribosome binds to begin translation
• C. A sequence that encodes a gene
• D. A sequence of nitrogen bases where RNA polymerase attaches to begin transcription

Answer: (D)

Promoters are DNA sequences that control transcription by providing the binding site for RNA polymerase (and the transcription machinery). They lie upstream of a gene and determine where RNA polymerase attaches and where transcription starts (the +1 site). In bacteria, promoter elements like the -35 and -10 boxes help RNA polymerase (often with a sigma factor) recognize the start, while in eukaryotes general transcription factors assemble at the promoter to recruit RNA polymerase II. This makes the promoter the correct description: it’s the sequence where RNA polymerase attaches to begin transcription. The other phrases refer to different steps or elements—termination signals stop transcription, ribosome binding sites initiate translation, and a coding sequence is what gets transcribed and translated, not the promoter itself.