Fig 3. ECF σ factors and the age of genomics.
With increasing availability of DNA sequence information, the genetic diversity of σ factors became appreciated. The ECF subgroup was identified in 1994 (inset from Lonetto et al., 1994), and 1995 marked the beginning of the era of bacterial genomics. By 2009, phylogenomics-based approaches revealed that ECF σ factors were a highly diverse and often numerically dominant subset of alternative σ factors that play major roles, in many cases yet to be determined, in bacterial gene regulation (inset from Staron et al., 2009).