The promoter of the operon has been located by transcript mapping using primer extension with reverse transcriptase. The surrounding nucleotide sequence has features characteristic of promoters under stringent and growth-rate-dependent regulation, namely a GC-rich discriminator next to the −10 hexamer, an upstream AT-rich sequence (the UP element) and potential FIS-binding sites. Transcriptional activity of the promoter was examined using transcriptional fusions to placed at a single chromosomal location. Expression from was reduced under stringent conditions and varied with growth rate. Growth-rate control was independent of guanine-mediated repression. A fusion in which the GC-rich discriminator was mutated by insertion of an AT-rich oligonucleotide was used to demonstrate the importance of this region in control. Both stringent and growth-rate-dependent controls were abolished by the mutation. Other potential regulatory signals in the vicinity of the promoter are a operator (binding site for the PurR repressor), a operator, a DnaA-binding site and a CRP/FNR-binding sequence. The promoter lies back-to-back with the promoter for (exonuclease VII), the two promoters being separated by only 20 bp.


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