Regulation of Escherichia coli purF. Analysis of the control region of a pur regulon gene.

Escherichia coli purF has been determined to be the distal gene of a polycistronic operon. The first gene of the purF operon encodes a hydrophobic 17.9-kDa protein of unknown function. Deletion analyses indicate that the 17.9-kDa protein plays no role in the regulation of purF in cis. mRNA hybridization studies establish that purF is regulated at the transcriptional level. Enzyme and mRNA levels are repressed 11-17-fold by excess adenine. A single mRNA start site at nucleotide +1 was identified for transcripts synthesized in vivo. Two sites, at +1 and approximately +30, were used for transcription initiation in vitro. The purF promoter is localized between nucleotides -96 and -7 with sequences upstream of -71 necessary for high level expression. Initial evidence suggests that transcription is subject to stringent control. Deletion analyses localize the purF control element to a region between nucleotides -71 and +35. A putative control site between nucleotides -35 to +3 strongly resembles a 5' flanking sequence in the co-regulated gene purM. This site contains an imperfect inverted repeat sequence that is characteristic of sites recognized by regulatory proteins and is a candidate for the purF operator. This is the first detailed analysis of a gene involved in de novo purine nucleotide biosynthesis.