L-arabinose operon

The L-arabinose operon of the model bacterium "Escherichia coli" has been a focus for research in molecular biology for over 40 years, and has been investigated extensively at the genetic, biochemical, physiological, and biophysical levels.It is controlled by a dual positive and negative system.There are 3 structural genes: "araB", "araA", and "araD". They encode the metabolic enzymes forbreaking down the monosaccharide sugar arabinose into D-xylulose-5-phosphate, which is then metabolised via the pentose phosphate pathway. The initiator region, containing an operator site as well as a promoter, is called "araI" (the last letter of "araI" is an uppercase letter " i ").Near this site lies the "araC" gene, which encodes an activator protein. The AraC protein binds to initiator region "araI".

Activation

If arabinose is present, it builds a complex: AraC + arabinose
This complex is needed for RNA polymerase to bind to the promoter and transcribe the "ara" operon.Also for activation the binding of another structure to "araI" is needed: CAP + cyclic AMP
So the activation depends on the presence of arabinose and cAMP.

Repression

If arabinose is absent, the AraC protein assumes a different conformation. In this conformationthe AraC protein binds as well to "araI" as to "ara0" region. Now the DNA is forming a loop. Thisprevents transcription of the "ara" operon.

Sequence of the Operon:

araC : araO : araI : araB : araA : araD

ee also

*The lac operon is another operon in "E. coli" that has been a focus for research in gene expression.

References

cite journal
last =
first = Robert Schleif
authorlink =
coauthors =
title = Regulation of the L-arabinose operon of "Escherichia coli"
journal = Trends in Genetics
volume = 16
issue = 12
pages = 559–565
publisher =
date = December 2000
url =
doi =
id =
accessdate =