The regulatory region of the biotin operon in Escherichia coli.

It is proposed that the biotin anabolic operon in Escherichia coli is transcribed divergently from two partially overlapping face-to-face promoters. A mutation that increases transcription in vivo creates an additional promoter in vitro. The putative operator contains an imperfect palindromic sequence that partially overlaps the promoters. The regulatory and genetic implications of these findings are discussed.