Transcriptional mapping and nucleotide sequence of the Escherichia coli fepA-fes enterobactin region. Identification of a unique iron-regulated bidirectional promoter.

The iron-controlled fepA and fes-entF transcripts from the Escherichia coli enterobactin gene complex are expressed divergently from a limited genetic region, thereby suggesting the existence of a single, possibly overlapping promoter junction for these genes. The nucleotide sequence of a 1,997-base pair HpaI fragment specific for this genetic region allowed for the identification of an 1,122-base pair open reading frame as the previously uncharacterized fes gene. Its product, Fes (approximately Mr 42,573) plays an essential but as yet ambiguous role in the release of ferric iron from the ligand. An additional small open reading frame of 216 nucleotides (encoding a potential product of calculated Mr 8,271) was also identified between fes and entF. A portion of the remaining nucleotide sequence defined a 320-base pair control region for both the fepA and fes-entF messages. Primer extension analyses placed the major in vivo transcription initiation sites to within 18 nucleotides of one another, thereby revealing a novel, extensively overlapping bidirectional promoter as well as long dual leader transcripts. This promoter region contains multiple overlapping nucleotide stretches which show strong homology to the consensus Fur repressor-binding sequence, forms of which are found in all E. coli iron-regulated promoters characterized to date.