The structural genes, which encode enzymes for arabinose catabolism, are araB, araA, and araD (collectively known as araBAD). The regulator gene is araC. The genes araBAD and araC are transcribed in opposite directions. [2]
araA encodes L-arabinose isomerase, which catalyzes isomerization between L-arabinose and L-ribulose.
araB encodes ribulokinase, which catalyzes phosphorylation of (L/D)-ribulose to form (L/D)-ribulose 5-phosphate.
araD encodes L-ribulose-5-phosphate 4-epimerase, which catalyzes epimerization between L-ribulose 5-phosphate and D-xylulose 5-phosphate.
D-xylulose 5-phosphate and D-ribulose-5-phosphate are metabolites in the pentose phosphate pathway.
The operators are araI and araO2. The operators lie between the AraC.
AraI lies between the structural genes and the operator. The araI1 and araI2 are DNA-binding sites that, when occupied by AraC, induce expression.
Sequence of the Operon
5' araC araO araI araB araA araD 3'
Regulator Operator Structural
(Distances not to scale)