This group dissipated from the ECF classification during the reclassification by [[Casas-Pastor et al.]]!
ECF101 σ factors were found in members of the phyla Actinobacteria and Proteobacteria (Staroń et al., 2009).
In this group genomic context conservation does not extend beyond those genes encoding the σ factor and its cognate anti-σ factor.
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.
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.