title: 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.
abstract: 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.
authors: Department of Biology, University of New Brunswick, Fredericton, NB, Canada.
authors: Xiaowei
authors: X
authors: Xue
authors: Department of Biology, University of New Brunswick, Fredericton, NB, Canada.
authors: Maria C
authors: MC
authors: Davis
authors: Department of Biology, University of New Brunswick, Fredericton, NB, Canada.
authors: Thomas
authors: T
authors: Steeves
authors: Department of Biology, University of New Brunswick, Fredericton, NB, Canada.
authors: Adam
authors: A
authors: Bishop
authors: Department of Biology, University of New Brunswick, Fredericton, NB, Canada.
authors: Jillian
authors: J
authors: Breen
authors: Department of Biology, University of New Brunswick, Fredericton, NB, Canada.
authors: Allison
authors: A
authors: MacEacheron
authors: Department of Biology, University of New Brunswick, Fredericton, NB, Canada.
authors: Christopher A
authors: CA
authors: Kesthely
authors: Department of Biology, University of New Brunswick, Fredericton, NB, Canada.
authors: FoSheng
authors: F
authors: Hsu
authors: Department of Biology, University of New Brunswick, Fredericton, NB, Canada.
authors: Shawn R
authors: SR
authors: MacLellan
mesh_terms: D000595:Amino Acid Sequence; D001412:Bacillus subtilis / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D012808:Sigma Factor / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D021122:Protein Subunits; D012808:Sigma Factor