Regulation of the araC gene of Escherichia coli: catabolite repression, autoregulation, and effect on araBAD expression.

The araC gene encodes a positive regulatory protein required for L-arabinose utilization in Escherichia coli. Transcription from the araC promoter has been shown to be under positive control by cAMP receptor protein and under negative control by its protein product (autoregulation). This work describes the identification of the region of the araC promoter that interacts with the cAMP receptor protein to mediate catabolite repression. A 3-base-pair deletion centered 60 base pairs from the transcriptional initiation site results in a mutant araC promoter that, in the absence of araC protein, reduces transcriptional activity when compared with the wild-type promoter and is unresponsive to various concentrations of intracellular cAMP in vivo. The same deletion results in a lowered affinity of the araC promoter for cAMP receptor protein in vitro. However, this lowered affinity for the mutant araC promoter does not result in substantial reduction of intracellular araC protein because autoregulation of the araC gene dominates catabolite repression. The 3-base-pair deletion in the cAMP receptor protein binding site of the araC promoter does not affect catabolite repression of the adjacent araBAD operon. The implications of these results on current models for expression of the araBAD operon and the araC gene are discussed.