Identification and DNA sequence of tdcR, a positive regulatory gene of the tdc operon of Escherichia coli.

Efficient in vivo expression of the biodegradative threonine dehydratase (tdc) operon of Escherichia coli is dependent on a regulatory gene, tdcR. The tdcR gene is located 198 base pairs upstream of the tdc operon and is transcribed divergently from this operon. The nucleotide sequence of tdcR and two unrelated reading frames has been determined. The deduced amino acid sequence of TdcR indicates that it is a polypeptide of Mr 12,000 with 99 amino acid residues and contains a potential helix-turn-helix DNA binding motif. Deletion analysis and minicell expression of the tdcR gene suggest that TdcR may serve as a trans-acting positive activator for the tdc operon.