The Escherichia coli melAB promoter has been cloned on a short DNA fragment and subjected to deletion mutagenesis, random mutagenesis and site-directed mutagenesis. In previous work we had shown that expression from the melAB promoter is triggered by melibiose and that this requires the MelR transcription activator. Melibiose-dependent expression is suppressed by deletions that remove both DNA-binding sites for MelR and by point mutations in the -10 hexamer, the -35 hexamer and the region just upstream of the -35 hexamer. The point mutations identify promoter elements that are essential for triggering the melAB promoter. The importance of these elements was confirmed by site-directed mutagenesis. The results show that the organization of the melAB promoter is fundamentally different from the organization of other bacterial promoters controlled by homologues of MelR.

This content is only available as a PDF.
You do not currently have access to this content.