Nucleotide sequence and organisation of the gua promoter region of Escherichia coli.

Overlapping restriction fragments of DNA carrying the gua promoter region of Escherichia coli have been cloned using promoter-probe plasmids. Antibiotic resistance conferred by the constructed plasmids is repressed by guanine and enhanced by adenine, two features characteristic of expression of the gua operon. The nucleotide sequence of these fragments reveals the gua promoter 43 bp upstream of the translational start codon for inosine 5'-monophosphate (IMP) dehydrogenase. The promoter is preceded by an A + T-rich region and several potential polymerase secondary binding sites, and is immediately followed by a G + C-rich discriminator, suggesting that the gua operon may be under stringent control. A sequence with twofold symmetry overlaps both promoter and discriminator and is therefore located where repressor binding could interfere with transcription initiation. A stem and loop can be formed from the leader mRNA, thus sequestering the ribosome-binding site.