title: SlrA/SinR/SlrR inhibits motility gene expression upstream of a hypersensitive and hysteretic switch at the level of σ(D)  in Bacillus subtilis.
abstract: Exponentially growing Bacillus subtilis cultures are epigenetically differentiated into two subpopulations in which cells are either ON or OFF for σ(d) -dependent gene expression: a pattern suggestive of bistability. The gene encoding σ(D) , sigD, is part of the 31-gene fla/che operon where its location at the 3' end, 25 kb away from the strong P(fla/che) promoter, determines its expression level relative to a threshold. Here we show that addition of a single extra copy of the slrA gene in the chromosome inhibited σ(d) -dependent gene expression. SlrA together with SinR and SlrR reduced sigD transcript by potentiating a distance-dependent decrease in fla/che operon transcript abundance that was not mediated by changes in expression from the P(fla/che) promoter. Consistent with acting upstream of σ(D) , SlrA/SinR/SlrR was bypassed by artificial ectopic expression of sigD and hysteretically maintained for 20 generations by engaging the sigD gene at the native locus. SlrA/SinR/SlrR was also bypassed by increasing fla/che transcription and resulted in a hypersensitive output in flagellin expression. Thus, flagellin gene expression demonstrated hypersensitivity and hysteresis and we conclude that σ(d) -dependent gene expression is bistable.
authors.affiliation: Indiana University, Department of Biology, Bloomington, IN 47405, USA.
authors.forename: Loralyn M
authors.initials: LM
authors.lastname: Cozy
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Phillips
authors.forename: Rebecca A
authors.initials: RA
authors.lastname: Calvo
authors.forename: Ashley R
authors.initials: AR
authors.lastname: Bate
authors.forename: Yi-Huang
authors.initials: YH
authors.lastname: Hsueh
authors.forename: Richard
authors.initials: R
authors.lastname: Bonneau
authors.forename: Patrick
authors.initials: P
authors.lastname: Eichenberger
authors.forename: Daniel B
authors.initials: DB
authors.lastname: Kearns
mesh_terms: D001412:Bacillus subtilis / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D015536:Down-Regulation; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D009876:Operon; D011401:Promoter Regions, Genetic; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D012808:Sigma Factor