Describe negative and positive transcriptional control of the ARA operon in E.coli
1-Arabinose not preseent (repressor).(Negative control) AraC binds araI and another binds araO2. These two bend DNA, preventing RNA poly from binding to the promoter of the ARA operon, stoping transcription. AraC is the repressor here.
2-Arabinose is present (activator). (Positive control)Arabinose binds to AraC and prevents the molecules from interacting, breaking the DNA loop. the binding of the two AraC complexes to the araI site promotes transcription. So when Arabinose is present AraC is an activator.