What happens when arabinose is present in the system?

What happens when arabinose is present in the system?

• A. Arabinose binds to AraC, enabling RNA polymerase to transcribe the rfp gene.
• B. Arabinose inhibits transcription of rfp.
• C. Arabinose degrades the plasmid.
• D. Arabinose activates ampicillin resistance.

Answer: (A)

Arabinose acts as an inducer for the arabinose-regulated expression system. When arabinose is present, it binds to the AraC protein and changes AraC’s shape so it promotes transcription rather than blocking it. This enables RNA polymerase to initiate transcription from the pBAD promoter, leading to expression of the downstream rfp gene and production of red fluorescent protein. Without arabinose, AraC represses transcription at this promoter, so rfp is not expressed. The other options don’t fit because arabinose doesn’t inhibit transcription, degrade the plasmid, or activate antibiotic resistance in this setup.

Arabinose acts as an inducer for the arabinose-regulated expression system. When arabinose is present, it binds to the AraC protein and changes AraC’s shape so it promotes transcription rather than blocking it. This enables RNA polymerase to initiate transcription from the pBAD promoter, leading to expression of the downstream rfp gene and production of red fluorescent protein. Without arabinose, AraC represses transcription at this promoter, so rfp is not expressed. The other options don’t fit because arabinose doesn’t inhibit transcription, degrade the plasmid, or activate antibiotic resistance in this setup.