The arabinose system enables E. coli and its relatives to take up the pentose -arabinose from the growth medium using products of the unlinked araE and araFGH genes, and then convert intracellular arabinose in three steps catalyzed by the products of the araBAD genes to -xylulose-5-phosphate. This then enters the pentose phosphate shunt. AraC protein regulates expression of its own synthesis and the other genes of the ara system. In the presence of arabinose, AraC stimulates initiation of mRNA synthesis from the promoters pE, pFGH, pBAD 10. J. Johnson and R. Schleif, In vivo induction kinetics of the arabinose promoters in Escherichia coli. J. Bacteriol. 177 (1995), pp. 3 and pJ, a promoter serving a gene of unknown function. At pBAD, the AraC protein not only acts positively to stimulate transcription in the presence of arabinose, but also acts negatively in the absence of arabinose to repress transcription initiation; whereas at pC, AraC acts negatively in the presence or absence of arabinose.
