Organisation of the regulatory region of the Escherichia coli melibiose operon.

The regulatory region of the Escherichia coli melibiose operon contains two divergent promoters. One promoter is responsible for the expression of the melR gene, that is essential for melibiose-dependent stimulation of the second promoter. Melibiose-induced transcription from this second promoter initiates at a start point 25 bp upstream from the start codon of the melA gene, encoding an alpha-galactosidase. The nucleotide sequence covering the divergent promoters and the melR gene is reported.