Which statement about arabinose presence and AraC function is true?

Which statement about arabinose presence and AraC function is true?

• A. It binds arabinose causing AraC to repress PBAD
• B. It binds arabinose causing AraC to activate PBAD by promoting RNA polymerase binding
• C. It causes AraC to change conformation, enabling the AraC–RNA polymerase complex to activate transcription from PBAD
• D. It has no effect on PBAD transcription

Answer: (C)

Arabinose sensing by AraC changes the regulatory outcome at PBAD. When arabinose is present, AraC undergoes a conformational shift that enables it to form an active complex with RNA polymerase at PBAD, turning transcription on. In this activated state, AraC–RNA polymerase can efficiently recruit the polymerase to initiate transcription from PBAD. Without arabinose, AraC binds in a way that promotes DNA looping and represses transcription. So the correct statement reflects that arabinose binding changes AraC’s shape to enable the AraC–RNA polymerase complex to activate transcription from PBAD. The other options either suggest repression in the presence of arabinose, oversimplify the mechanism as just promoting RNA polymerase binding, or claim there is no effect at all.

Arabinose sensing by AraC changes the regulatory outcome at PBAD. When arabinose is present, AraC undergoes a conformational shift that enables it to form an active complex with RNA polymerase at PBAD, turning transcription on. In this activated state, AraC–RNA polymerase can efficiently recruit the polymerase to initiate transcription from PBAD. Without arabinose, AraC binds in a way that promotes DNA looping and represses transcription. So the correct statement reflects that arabinose binding changes AraC’s shape to enable the AraC–RNA polymerase complex to activate transcription from PBAD. The other options either suggest repression in the presence of arabinose, oversimplify the mechanism as just promoting RNA polymerase binding, or claim there is no effect at all.