%0 Journal Article %A Xue, Xiaowei %A Davis, Maria C. %A Steeves, Thomas %A Bishop, Adam %A Breen, Jillian %A MacEacheron, Allison %A Kesthely, Christopher A. %A Hsu, FoSheng %A MacLellan, Shawn R. %T Characterization of a protein–protein interaction within the SigO–RsoA two-subunit σ factor: the σ70 region 2.3-like segment of RsoA mediates interaction with SigO %D 2016 %J Microbiology, %V 162 %N 10 %P 1857-1869 %@ 1465-2080 %R https://doi.org/10.1099/mic.0.000358 %K protein–protein interaction %K Bacillus subtilis %K sigma factor %K RNA polymerase %K transcription %I Microbiology Society, %X σ factors are single subunit general transcription factors that reversibly bind core RNA polymerase and mediate gene-specific transcription in bacteria. Previously, an atypical two-subunit σ factor was identified that activates transcription from a group of related promoters in Bacillus subtilis. Both of the subunits, named SigO and RsoA, share primary sequence similarity with the canonical σ70 family of σ factors and interact with each other and with RNA polymerase subunits. Here we show that the σ70 region 2.3-like segment of RsoA is unexpectedly sufficient for interaction with the amino-terminus of SigO and the β′ subunit. A mutational analysis of RsoA identified aromatic residues conserved amongst all RsoA homologues, and often amongst canonical σ factors, that are particularly important for the SigO–RsoA interaction. In a canonical σ factor, region 2.3 amino acids bind non-template strand DNA, trapping the promoter in a single-stranded state required for initiation of transcription. Accordingly, we speculate that RsoA region 2.3 protein-binding activity likely arose from a motif that, at least in its ancestral protein, participated in DNA-binding interactions. %U https://www.microbiologyresearch.org/content/journal/micro/10.1099/mic.0.000358