FIG 1.

Promoter region of pfeT. (A) Sequence logo of the Fur and PerR consensus operator sites. A total of 23 Fur and 11 Per sites was used to generate the sequence logos with WebLogo. The list of sequences is found in Tables S3 and S4 in the supplemental material. (B) The sequence of the pfeT promoter region contains one conserved PerR box (gray), named PerR I (PI), which is adjacent to the −35 region. Two Fur operator sites (bold), named Fur II (FII) and Fur III (FIII), are positioned both upstream and downstream of the Per site. FII is separated by 8 bp from the PerR box, while FIII is more than 55 bp downstream of the transcriptional start site. The transcriptional start site is denoted in bold. The −10 and −35 RNAP binding sites are in italics. Vertical lines (|) indicate conserved bases, and asterisks indicate mutated bases in the constructs containing operator site mutations. (C) Model for the pfeT control region (i), illustrating transcriptional repression by PerR (PDB accession number 3F8N) binding at sites PI and FII (ii) and induction by iron mediated by Fur (represented by the homolog Streptomyces coelicolor Zur; PDB code 3MWM) binding at FII (to antagonize PerR repression and as a direct transcription activator) and/or FIII (as a transcription activator) (iii).