What is the function of a promoter region?

• A. A DNA sequence that codes for a protein.
• B. A DNA sequence where RNA polymerase binds to start transcription.
• C. A protein that unwinds DNA to begin replication.
• D. A region that terminates transcription.

Answer: (B)

The promoter region is the DNA sequence that signals where transcription should begin by providing a binding site for RNA polymerase (and the necessary transcription factors). It acts as the on switch for a gene, helping RNA polymerase assemble at the correct start site and initiate RNA synthesis. It sits upstream of the coding region and does not itself encode a protein. That’s why its main function is to recruit the transcription machinery and set the stage for gene expression. This differs from coding regions, which contain the instructions to make a protein; from helicases that unwind DNA during replication; and from terminator sequences that stop transcription.