AraC serves as an activator and as a repressor

Dual control of the ara operon. (a) In the presence of arabinose, the AraC protein binds to the araI region. The CAP-cAMP complex binds to a site adjacent to araI. This binding stimulates the transcription of the araB, araA, and araD genes. (b) In the absence of arabinose, the AraC protein binds to both the araI and the araO regions, forming a DNA loop. This binding prevents transcription of the ara operon.