Which promoter controls expression of the red fluorescent protein in the presence of arabinose?

Which promoter controls expression of the red fluorescent protein in the presence of arabinose?

• A. The arabinose-inducible promoter (Pbad) activated by araC in the presence of arabinose.
• B. The lac promoter.
• C. The T7 promoter.
• D. The trp promoter.

Answer: (A)

Arabinose control of gene expression via the Pbad promoter is the concept here. In this system, the AraC protein senses arabinose and, when arabinose is present, AraC changes shape to activate transcription from Pbad. Placing the red fluorescent protein gene under this promoter means the protein is produced only when arabinose is around, giving you fluorescence on the condition that arabinose is present. Without arabinose, AraC keeps Pbad off, so there’s little or no red fluorescence. The other promoters work by different regulators: the lac promoter is turned on by lactose or IPTG and controlled by LacI; the T7 promoter needs T7 RNA polymerase to drive transcription; the trp promoter responds to tryptophan levels via the Trp repressor. Thus, only the arabinose-responsive promoter matches the scenario.

Arabinose control of gene expression via the Pbad promoter is the concept here. In this system, the AraC protein senses arabinose and, when arabinose is present, AraC changes shape to activate transcription from Pbad. Placing the red fluorescent protein gene under this promoter means the protein is produced only when arabinose is around, giving you fluorescence on the condition that arabinose is present. Without arabinose, AraC keeps Pbad off, so there’s little or no red fluorescence.

The other promoters work by different regulators: the lac promoter is turned on by lactose or IPTG and controlled by LacI; the T7 promoter needs T7 RNA polymerase to drive transcription; the trp promoter responds to tryptophan levels via the Trp repressor. Thus, only the arabinose-responsive promoter matches the scenario.