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Ara operon
The L-arabinose operon contains three structural genes - araB, araA, and araD - that encode enzymes required for the metabolism of L-arabinose in E. coli. The expression of the operon is regulated by the AraC protein and the CAP-cAMP complex. In the absence of L-arabinose, AraC acts as a repressor by forming a DNA loop, while in the presence of L-arabinose, AraC binds to different DNA sites and activates transcription. CAP facilitates activation when glucose is absent. The operon is also used in protein expression systems by fusing genes of interest to the araBAD promoter.
