Which region serves as the binding site for RNA polymerase to initiate transcription in a prokaryote?

• A. Promoter
• B. Operator
• C. Enhancer
• D. Terminator

Answer: (A)

In prokaryotes, transcription starts when RNA polymerase holoenzyme binds to a promoter region upstream of the gene. The promoter contains conserved sequences, such as the -35 and -10 boxes, that the sigma factor recognizes, guiding the polymerase to the correct start site and helping it open the DNA to begin RNA synthesis at the +1 position. The promoter is the specific binding site that initiates transcription. In contrast, the operator is a regulatory site where repressors can block access to the promoter, enhancers are regulatory elements that boost transcription in some contexts (more common in eukaryotes), and terminators signal the end of transcription.