Nucleotide sequence of the ilvB promoter-regulatory region: a biosynthetic operon controlled by attenuation and cyclic AMP.

The DNA sequence of the promoter-regulatory region of the ilvB operon of Escherichia coli was determined. This region encodes a potential leader polypeptide containing 32 amino acids, 12 of which are the regulatory amino acids valine and leucine. Approximately 50 residues downstream from the coding region for the potential leader peptide is a site for terminating transcription. In vitro transcription experiments show that transcription terminates at this site and produces a leader mRNA of approximately equal to 188 nucleotides. A model for the multivalent regulation of this operon by valyl- and leucyl-tRNA is proposed on the basis of the mutually exclusive formation of five strong stem-and-loop structures in the leader mRNA. In addition, the -35 and -70 regions of this sequence show close structural homologies to areas in cyclic AMP receptor protein (CRP)-dependent promoters reported to be important for CRP function. In vitro transcription from the ilvB promoter was greatly increased by cyclic AMP and CRP. Taken together, these data strongly suggest that the ilvB biosynthetic operon is negatively controlled by multivalent transcription termination and is positively regulated by cyclic AMP and CRP.