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

Taxonomical distribution

ECF101 σ factors were found in members of the phyla Actinobacteria and Proteobacteria (Staroń et al., 2009).

Experimentally studied examples


Genomic context conservation

In this group genomic context conservation does not extend beyond those genes encoding the σ factor and its cognate anti-σ factor.

Signaling mechanism

The cognate anti-σ factors of ECF101 σ factors are predicted soluble proteins that contain a ZAS domain (Staroń et al., 2009). This domain coordinates the binding of Zn2+ to the protein and is responsible for conformational changes that depend on the binding of the ion (Zdanowski et al., 2006). This suggests that the activity of ECF101 σ factors is regulated through conformational changes of the soluble anti-σ factors. Experimental evidence to support this hypothesis is still missing for this ECF group.

Physiological function



Members of original ECF101 are part of ECF293 together with original groups ECF13 and ECF117. 11.35% of the proteins from ECF293 have homology to original ECF101.


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.
Zdanowski K, Doughty P, Jakimowicz P, O’Hara L, Buttner MJ, et al. 2006. Assignment of the zinc ligands in RsrA, a redox-sensing ZAS protein from Streptomyces coelicolor. Biochemistry 45 (27): 8294–8300.
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