Nucleotide sequence of putC, the regulatory region for the put regulon of Escherichia coli K12.

The nucleotide sequence of the putC region, from which divergent transcription of the putP and putA genes starts, was determined. The promoter region for the putA gene was restricted to the location between the HindIII site and the NcoI site or at the NcoI site by using putA-lacZ fusion plasmids and the transcriptional start for the putA gene was identified in the region between the HindIII site and the NcoI site by Sl mapping. This region also contains a potential CAP binding site, a ribosome binding site, and a sequence that is highly homologous to argTr. Five potential promoters (putPp1-putPp5) for the putP gene, which were separate from the promoter region for the putA gene, were indicated by S1 mapping analysis of the putP gene transcripts. We concluded that the putC region is 419 bp long and contains two independent sets of promoters, regulating the expression of putP and putA genes in opposite directions. In addition, this region was found to contain an open reading frame (orf) capable of encoding a polypeptide of 111 amino acids in overlapping fashion. But studies using an orf-lacZ fusion gene showed that this open reading frame was not expressed.