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In vivo induction kinetics of the arabinose promoters in Escherichia coli

In Escherichia coli, the AraC protein represses transcription from its own promoter, PC, and when associated with arabinose, activates transcription from three other promoters, PBAD, PE, and PFGH. Expression from all four of these promoters is also regulated by cyclic AMP-catabolite activator protein; however, the arrangement of the protein binding sites is not identical for each promoter. We are interested in determining how the AraC protein is able to activate PBAD, PE, and PFGH despite their differences. We have characterized the induction response of the wild-type arabinose operons from their native chromosomal locations by primer extension analysis. In this analysis, mRNA from the four arabinose operons plus an internal standard could all be assayed in the RNA obtained from a single sample of cells. We found that each of the operons shows a rapid, within 15 to 30 s, response to arabinose. We also found that the expression of araFGH is more sensitive to catabolite repression but not to arabinose concentration than are araE and araBAD. Finally, we have determined the relative levels of inducibility in wild-type cells of araBAD, araFGH, and araE to be 6.5, 5, and 1, respectively. These results provide a basis for subsequent studies to determine the mechanism(s) by which AraC protein activates transcription from the different arabinose promoters.