Novel activation of araC expression and a DNA site required for araC autoregulation in Escherichia coli B/r

Mutations in the araC gene have been isolated which alter both the activator and autoregulatory functions of AraC protein (L.G. Cass and G. Wilcox, J. Bacteriol. 166:892-900, 1986). In this study, the effect of each araC mutation on autoregulation was characterized in vivo and in vitro in the presence of L-arabinose. The effect of L-arabinose in some of these araC mutants revealed a novel activation of araC expression which was not observed in the araC+ cell. Experiments were therefore focused on understanding the mechanism of this novel activation. We describe a systematic analysis of the effect of mutations within the known regulatory binding sites for araBAD and araC transcription on araC expression. Our results suggest that the novel activation of araC expression requires the AraC activator-binding site, araI, and the cyclic AMP receptor protein-cyclic AMP complex-binding site. We also found that in the absence of L-arabinose, the araI site was required for maximal autoregulation by the wild-type AraC protein.