The Escherichia coli melR gene encodes a DNA-binding protein with affinity for specific sequences located in the melibiose-operon regulatory region.

Crude extracts, made from Escherichia coli cells carrying a plasmid in which the melR gene was expressed from the galP2 promoter, were used as a source of MelR protein. Using DNase I footprinting and gel retardation assays, we show that MelR binds to two sites located from nucleotides (nt) -49 to -75 and -85 to -113, upstream from the melAB transcription start point. The two sites contain identical 18-bp sequences. Specific binding is unaltered by deletions that remove 1 or 6 amino acids (aa) from the C terminus of MelR, but is abolished by deletion of 16, 24 or more aa residues. Sequence homologies between MelR and other DNA-binding proteins are discussed.