This group dissipated from the ECF classification during the reclassification by [[Casas-Pastor et al.]]!

Taxonomical distribution

Members of the ECF group ECF05 are restricted to Proteobacteria (Staroń et al., 2009).

Experimentally studied examples

The two best-studied members of this group are E. coli FecI (Braun and Mahren, 2005) and Bordetella pertussis HurI (Vanderpool and Armstrong, 2003).

Genomic context conservation

Members of this group show extended genomic context conservation, with genes encoding outer membrane proteins located downstream of the transcriptional unit encoding the ECF σ/anti-σ factor (Staroń et al., 2009).

Signaling mechanism

In this group, regulation of ECF σ factor activity is regulated through protein-protein interaction cascades. In the absence of the inducing stimulus, the ECF σ factor is kept inactive by its cognate membrane-associated anti-σ factor, which contain a N-terminal ASD and a C-terminal FecR domain (Staroń et al., 2009). Under inducing condition, i.e. when a substrate is bound to the corresponding outer membrane protein, the σ factor is released from the anti-σ factor and is then free to initiate transcription from its target promoters (Braun and Mahren, 2005). Remarkably, and in contrast to most other ECF σ factors, members of this group do not seem to autoregulate their own expression. Instead, expression of these ECF σ factors is under the control of the Fur master regulator, which coordinates the cellular responses to intracellular iron limitation, in which these ECF σ factors play a role (Escolar et al., 1999). Group ECF05 is highly similar to groups ECF06-ECF08 and ECF10 and many features described for this group hold also true for the phylogenetically related groups, including lack of autoregulation, the genomic context conservation and the target promoter motif.

Physiological function

These extensively studied ECF σ factors are involved in siderophore-mediated iron uptake (Mettrick and Lamont, 2009).


This group is now part of ECF243 (FecI-like group). 45.1% of the proteins from ECF243 have homology to original ECF05. ECF243 merges original ECF05-09.


Braun V, Mahren S. 2005. Transmembrane transcriptional control (surface signalling) of the Escherichia coli Fec type. FEMS Microbiology Reviews 29 (4): 673–684.
Escolar L, Pérez-Martín J, de Lorenzo V. 1999. Opening the iron box: transcriptional metalloregulation by the Fur protein. Journal of Bacteriology 181 (20): 6223-6229.
Mettrick KA, Lamont IL. 2009. Different roles for anti-sigma factors in siderophore signalling pathways of Pseudomonas aeruginosa. Molecular Microbiology 74 (5): 1257–1271.
Staroń A, Sofia HJ, Dietrich S, Ulrich LE, Liesegang H, et al. 2009. The third pillar of bacterial signal transduction: classification of the extracytoplasmic function (ECF) sigma factor protein family. Molecular Microbiology 74 (3): 557–581.
Vanderpool CK, Armstrong SK. 2003. Heme-responsive transcriptional activation of Bordetella bhu genes. Journal of Bacteriology 185 (3): 909–917.
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