RESUMEN
Endospore formation by Bacillus subtilis involves three differentiating cell types, the predivisional cell, the mother cell, and the forespore. Here we report the program of gene expression in the forespore, which is governed by the RNA polymerase sigma factors sigma(F) and sigma(G) and the DNA-binding proteins RsfA and SpoVT. The sigma(F) factor turns on about 48 genes, including the gene for RsfA, which represses a gene in the sigma(F) regulon, and the gene for sigma(G). The sigma(G) factor newly activates 81 genes, including the gene for SpoVT, which turns on (in nine cases) or stimulates (in 11 cases) the expression of 20 genes that had been turned on by sigma(G) and represses the expression of 27 others. The forespore line of gene expression consists of many genes that contribute to morphogenesis and to the resistance and germination properties of the spore but few that have metabolic functions. Comparative genomics reveals a core of genes in the sigma(F) and sigma(G) regulons that are widely conserved among endospore-forming species but are absent from closely related, but non-spore-forming Listeria spp. Two such partially conserved genes (ykoU and ykoV), which are members of the sigma(G) regulon, are shown to confer dry-heat resistance to dormant spores. The ykoV gene product, a homolog of the non-homologous end-joining protein Ku, is shown to associate with the nucleoid during germination. Extending earlier work on gene expression in the predivisional cell and the mother cell, we present an integrated overview of the entire program of sporulation gene expression.
Asunto(s)
Bacillus subtilis/genética , Regulación Bacteriana de la Expresión Génica/genética , Esporas Bacterianas/genética , Proteínas Bacterianas/genética , Proteínas Bacterianas/metabolismo , Secuencia de Bases , Biología Computacional , Daño del ADN/genética , Reparación del ADN/genética , Perfilación de la Expresión Génica , Genoma Bacteriano/genética , Genómica , Calor , Peróxido de Hidrógeno/farmacología , Datos de Secuencia Molecular , Regiones Promotoras Genéticas/genética , Transporte de Proteínas , Proteínas Recombinantes de Fusión/metabolismo , Regulón/genética , Factor sigma/química , Factor sigma/metabolismo , Esporas Bacterianas/efectos de los fármacos , Esporas Bacterianas/metabolismo , Esporas Bacterianas/efectos de la radiación , Transcripción GenéticaRESUMEN
Asymmetric division during sporulation by Bacillus subtilis generates a mother cell that undergoes a 5-h program of differentiation. The program is governed by a hierarchical cascade consisting of the transcription factors: sigma(E), sigma(K), GerE, GerR, and SpoIIID. The program consists of the activation and repression of 383 genes. The sigma(E) factor turns on 262 genes, including those for GerR and SpoIIID. These DNA-binding proteins downregulate almost half of the genes in the sigma(E) regulon. In addition, SpoIIID turns on ten genes, including genes involved in the appearance of sigma(K). Next, sigma(K) activates 75 additional genes, including that for GerE. This DNA-binding protein, in turn, represses half of the genes that had been activated by sigma(K) while switching on a final set of 36 genes. Evidence is presented that repression and activation contribute to proper morphogenesis. The program of gene expression is driven forward by its hierarchical organization and by the repressive effects of the DNA-binding proteins. The logic of the program is that of a linked series of feed-forward loops, which generate successive pulses of gene transcription. Similar regulatory circuits could be a common feature of other systems of cellular differentiation.
Asunto(s)
Bacillus subtilis/genética , Bacillus subtilis/fisiología , Regulación Bacteriana de la Expresión Génica , Regulación de la Expresión Génica , Esporas Bacterianas/química , Transcripción Genética , Secuencias de Aminoácidos , Fenómenos Fisiológicos Bacterianos , Proteínas Bacterianas/química , Proteínas Bacterianas/genética , Sitios de Unión , Inmunoprecipitación de Cromatina , Mapeo Cromosómico , Biología Computacional/métodos , ADN/química , ADN/genética , Desoxirribonucleasa I/metabolismo , Regulación hacia Abajo , Genes Bacterianos , Modelos Genéticos , Modelos Estadísticos , Datos de Secuencia Molecular , Análisis de Secuencia por Matrices de Oligonucleótidos , Plásmidos/metabolismo , Reacción en Cadena de la Polimerasa , Regiones Promotoras Genéticas , Unión Proteica , beta-Galactosidasa/metabolismoRESUMEN
Filamentous soil bacteria of the genus Streptomyces carry out complex developmental cycles that result in sporulation and production of numerous secondary metabolites with pharmaceutically important activities. To further characterize the molecular basis of these developmental events, we screened for mutants of Streptomyces coelicolor that exhibit aberrant morphological differentiation and/or secondary metabolite production. On the basis of this screening analysis and the subsequent complementation analysis of the mutants obtained we assigned developmental roles to a gene involved in methionine biosynthesis (metH) and two previously uncharacterized genes (SCO6938 and SCO2525) and we reidentified two previously described developmental genes (bldA and bldM). In contrast to most previously studied genes involved in development, the genes newly identified in the present study all appear to encode biosynthetic enzymes instead of regulatory proteins. The MetH methionine synthase appears to be required for conversion of aerial hyphae into chains of spores, SCO6938 is a probable acyl coenzyme A dehydrogenase that contributes to the proper timing of aerial mycelium formation and antibiotic production, and SCO2525 is a putative methyltransferase that influences various aspects of colony growth and development.
