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

Taxonomical distribution

σ factors of this group can only be found in organisms of the phylum Actinobacteria (Huang et al., 2015).

Experimentally studied examples


Genomic context conservation

ECF126 σ factor encoding genes are frequently located in the immediate vicinity of those encoding their cognate anti-σ factor, a putative anti-anti-σ factor and a calcium-binding protein (Huang et al., 2015).

Signaling mechanism

The ECF126 cognate putative anti-σ factors are long and soluble proteins, containing an N-terminal ZAS domain and C-terminally a domain similar to the N-terminal domain of the mycothiol maleylpyruvate isomerase (Huang et al., 2015). This is suggestive of regulation of σ factor activity based on conformational changes of a soluble anti-σ factor. Nevertheless, experimental evidence to support this hypothesis is still missing.

Physiological function

The physiological function of these σ factors remains elusive.


Members of this group are part of new ECF19, together with original groups ECF19 and ECF34. 3.66% of the proteins of ECF19 have homology to original ECF126.


Huang X, Pinto D, Fritz G, Mascher T. 2015. Environmental Sensing in Actinobacteria: a Comprehensive Survey on the Signaling Capacity of This Phylum. Journal of Bacteriology 197:2517–2535.
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