Abstract
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.
Highlights
Theiron-controlled fepA and fes-entF transcripts cations to thepromoter of the pColV-K30-derived aerobactin from the Escherichia coli enterobactin gene complex operon [5] and to act as a corepressor with ferrous iron in are expressed divergently from a limited genetic re- vitro by specific binding to the promoter region of an aerogion, thereby suggestingthe existence of asingle, pos- bactin-lac2 operon fusion construction [6]
Further assesssibly overlapping promoter junction for these genes. ment of Fur’s repressor role in iron transport, as well as the Thenucleotidesequence of a 1,997-base pair HpaI delineation of other potential common and specific factors, fragment specific for this genetic region allowed for awaits similar characterization of the other genetic systems the identification of an 1,122-base pair open reading frame as the previously uncharacterized fes gene
For the enterobactin gene cluster, this process has been slowed by its physical size [7] and its complexity (14 defined complementation groups)
Summary
Bp Sau3A fragment containing the fes promoter and translational initiation site into the BamHI site of the plasmid vector pMC1403. For both messages, the appearance of the identical respective bands using RNA from low-iron grown cells lacking PITS21 A central AT-specific palindrome, 5"ATAATATTAT is present between these two start points Within this core region, the proposed -10 sequences, both 5'-TAATAT, overlap one anotherand are centered 10 and 11bp, respectively,upstream from the major fes-entF and fepA +1sites. This arrangement suggests the possibility that multiple Fur interactions are involved in the iron-regulated expression of these transcripts
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