title: High- and low-threshold genes in the Spo0A regulon of Bacillus subtilis.
abstract: The master regulator for entry into sporulation in Bacillus subtilis is the response regulator Spo0A, which directly governs the expression of about 121 genes. Using cells in which the synthesis of Spo0A was under the control of an inducible promoter or in which production of the regulatory protein was impaired by a promoter mutation, we found that sporulation required a high (threshold) level of Spo0A and that many genes in the regulon differentially responded to high and low doses of the regulator. We distinguished four categories of genes, as follows: (i) those that required a high level of Spo0A to be activated, (ii) those that required a high level of Spo0A to be repressed, (iii) those that were activated at a low level of the regulator, and (iv) those that were repressed at a low dose of the regulator. Genes that required a high dose of Spo0A to be activated were found to have low binding constants for the DNA-binding protein. Some genes that were turned on at a low dose of Spo0A either had a high binding constant for the regulatory protein or were activated by an indirect mechanism involving Spo0A-mediated relief of repression by the repressor protein AbrB. We propose that progressive increases in the level of Spo0A leads to an early phase of transcription in which genes that play auxiliary roles in development, such as cannibalism and biofilm formation, are turned on and a later phase in which genes that play a direct role in sporulation are activated.
authors.affiliation: Department of Molecular and Cellular Biology, Harvard University, 16 Divinity Ave., Cambridge, MA 02138, USA.
authors.forename: Masaya
authors.initials: M
authors.lastname: Fujita
authors.forename: José Eduardo
authors.initials: JE
authors.lastname: González-Pastor
authors.forename: Richard
authors.initials: R
authors.lastname: Losick
mesh_terms: D000222:Adaptation, Physiological; D019677:Artificial Gene Fusion; D001412:Bacillus subtilis / Q000737:chemistry / Q000502:physiology*; D001426:Bacterial Proteins / Q000032:analysis / Q000235:genetics* / Q000378:metabolism* / Q000502:physiology; D004268:DNA-Binding Proteins / Q000502:physiology; D024202:Electrophoretic Mobility Shift Assay; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics / Q000502:physiology*; D005798:Genes, Bacterial; D017930:Genes, Reporter; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D018085:Regulon; D015398:Signal Transduction; D013171:Spores, Bacterial / Q000235:genetics* / Q000254:growth & development; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism* / Q000502:physiology; D001616:beta-Galactosidase / Q000032:analysis / Q000235:genetics
chemical_list: C060762:AbrB protein, Bacillus subtilis; D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C080950:Spo0A protein, Bacillus subtilis; D014157:Transcription Factors; D001616:beta-Galactosidase