In a cloning plasmid, what is the role of the promoter?

• A. Drives transcription of the inserted gene.
• B. Initiates replication of the plasmid.
• C. Terminates transcription.
• D. Encodes antibiotic resistance.

Answer: (A)

Promoters are the DNA sequences where RNA polymerase binds to begin transcription. In a cloning plasmid, having a promoter upstream of the inserted gene means the cell’s transcription machinery is directed to transcribe that gene, producing mRNA that can be translated into the desired protein. This is why the promoter’s role is to drive transcription of the inserted gene. The other features have different jobs: the origin of replication starts plasmid replication, a terminator stops transcription, and an antibiotic resistance gene is used as a selectable marker rather than initiating transcription of the inserted gene.