Arabinose Operon

Consists of three juxtapositioned structural genes araB (l-ribulokinase), araA (L-arabinose isomerase) and araD (l-ribulose-4-epimerase) transcribed in this order into a polycistronic araBAD mRNA starting at the O ^BAD operator and initiated by the P ^BAD promoter. The repressor-activator site functions by positive or negative control and it is transcribed in the opposite direction from the O _C operator and uses the P _C promoter. These genes are near the beginning of the E. coli map, while another gene araF is located near map position 45. They form a common regulatory system: a regulon. The activation of the ara operon not only requires the presence of the substrate arabinose, but also that the catabolite activating protein cyclic adenosine monophosphate complex be attached to the promoter. This operon is subject to catabolite suppression and as long as glucose is present in the medium (even when arabinose is also available) its transcription cannot begin. operon, polycistronic, operator...