L-arabinose operon

The arabinose operon short ara operon is an operon, which plays an important role in the degradation of arabinose in bacteria, such as Escherichia coli. It consists of two promoters ( PC PBAD ), two operators ( araO1 and araO2 ), an inductor ( Arai ), consisting of I1 and I2, and three structural genes:

Operation

The ara- operon has four important regulatory regions by the regulator protein AraC (encoded by araC ), which can act both as Antiaktivator as well as the activator can be adjusted:

  • AraO1: is an operator; encoded by araC regulator protein, AraC can bind here and therefore suppresses the transcription of the promoter PC.
  • AraO2: is also an operator; the regulator protein is both this body and at Arai (more precisely, I1) attached, the transcription of PBAD is suppressed. In the absence of arabinose, AraC binds preferentially to araO2 and I1 to form a DNA loop is formed is inactivated by the PC. Also, can not bind to I1 and I2, so PBAD can not be activated as AraC.
  • Arai: is an inductor section; in the presence of arabinose, AraC support at this point (more precisely, I1 and I2) bound the activation of the PBAD transcription. In addition, the PC is now accessible promoter for RNA polymerase, and can be read.
  • CAP: CAP - binding site; forwards in the absence of simple sugars such as glucose CAP reordering AraC and inhibits the DNA loop formation and thus activates transcription of PBAD.

AraC suppresses its own expression in order to avoid excessive accumulation. This mechanism is referred to as autoregulation. If the concentration of araC, araO1 is free and the araC transcription starts again until a sufficient concentration value is reached.

In the presence of arabinose, this is bound by the regulator protein. Through allosteric change of the regulator protein that binds only to Arai and no longer araO2. In addition, no glucose present, binds the CAP protein to the CAP binding site, preventing the DNA loop formation and facilitates the binding of the regulatory protein to Arai.

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