What is the function of the PBAD element on the plasmid?

What is the function of the PBAD element on the plasmid?

• A. It acts as a transcription terminator that stops transcription after the gene
• B. It is the promoter used to drive expression of a downstream gene (e.g., rfp)
• C. It encodes a regulatory protein that controls transcription
• D. It is a site for replication initiation

Answer: (B)

PBAD is an inducible promoter located upstream of a gene on a plasmid. Its job is to recruit RNA polymerase and start transcription of the downstream gene, such as rfp. The activity of this promoter is controlled by the AraC regulator and the sugar arabinose: when arabinose is present, AraC enables transcription from PBAD and the downstream gene is expressed; in the absence of arabinose, PBAD activity is suppressed and expression is off. It’s not a terminator, it’s not encoding a regulatory protein itself, and it’s not a replication origin. This inducible promoter arrangement lets you turn gene expression on and off by adding arabinose, which is why a gene like RFP would be expressed only when arabinose is present.

PBAD is an inducible promoter located upstream of a gene on a plasmid. Its job is to recruit RNA polymerase and start transcription of the downstream gene, such as rfp. The activity of this promoter is controlled by the AraC regulator and the sugar arabinose: when arabinose is present, AraC enables transcription from PBAD and the downstream gene is expressed; in the absence of arabinose, PBAD activity is suppressed and expression is off. It’s not a terminator, it’s not encoding a regulatory protein itself, and it’s not a replication origin. This inducible promoter arrangement lets you turn gene expression on and off by adding arabinose, which is why a gene like RFP would be expressed only when arabinose is present.