FIG 6.

SigN distribution and phylogeny. (A) A phylogenetic tree indicating the relationships between members of the σ⁷⁰ family of proteins. Sigma factors of the σ⁷⁰ family were collected from 24 diverse bacterial genomes (Table S6). The colors represent which sigma factors were identified in the collection using the specified sigma factors from B. subtilis: gold, vegetative sigma, SigA (NCBI accession no. BAA25730.1); red, plasmid sigma, SigN (NCBI accession no. YP_008244202.1); green, stationary-phase sigma, SigH (NCBI accession no. QCJ19226.1); purple, extracytoplasmic (ECF) sigma, SigM (NCBI accession no. NP_388833.1). The relative location of SigN is labeled in black. The relative locations of other B. subtilis sigma factors are labeled in gray. Black dots indicate the locations of branches with bootstrap values greater than 70%. SigN homologs may represent a novel class of alternative σ⁷⁰ sigma factors, but we cannot conclude this with certainty from the present analysis due to the absence of strong bootstrap values in the deepest branches of the tree. The tree can be visualized online at https://itol.embl.de/tree/1401827363250201560954077. (B) A pie chart indicating the frequency of sigma factors encoded on plasmids relative to the total number of plasmid-encoded proteins taken from a set of over 6,000 naturally occurring plasmids (34). The number of each class is given as an absolute value and as a percentage divided by all of the proteins encoded from the plasmid collection.