Nucleotide sequence of the ilvB multivalent attenuator region of Escherichia coli K12.

The ilvB gene of Escherichia coli K12 has been cloned into a multicopy plasmid. The regulation of the cloned gene by valine or leucine limitation and by catabolite repression is the same as for the chromosome encoded gene. The nucleotide sequence of a regulatory region preceding the ilvB structural gene has been determined. This DNA sequence includes a promoter, a region which codes for a putative 32 amino acid polypeptide containing multiple valine and leucine codons, and a transcription termination site. In vitro transcription of this region produces a 184 nucleotide terminated leader transcript. Mutually exclusive secondary structures of the leader transcript are predicted. On the basis of these data, a model for multivalent attenuation of the ilvB operon is presented. Data are presented which suggests that at least part of the postulated CRP-cyclic AMP binding site of the ilvB operon precedes the transcription start site by more than 71 base pairs.