Analysis of the ferric citrate transport gene promoter of Escherichia coli.

FecI, an extracytoplasmic-function sigma factor, is required for initiation of transcription of the ferric citrate transport genes. A mutational analysis of the fecA promoter revealed that the nonconserved -10 region and a downstream regulatory element are important for fecA promoter activity. However, nucleotide substitutions in the well-conserved -35 region also have an effect on the fecA promoter activity. Titration of FecI suggests that the FecI-RNA polymerase holoenzyme does not bind strongly to the downstream regulatory element, which is therefore probably involved in a subsequent step of transcription initiation.