As the bacterium Bacillus subtilis differentiates from the vegetative form into a dormant endospore, complex morphological and physiological changes occur that require the expression of many genes. During the process, four new RNA polymerase sigma subunits appear displacing one another and conferring on the RNA polymerase different specificities for the recognition of different classes of promoters. These sigma factors appear in the order sigmaF, sigmaE, sigmaG, and sigmaK. In addition, the action of RNA polymerase on specific promoters is controlled by DNA binding proteins to affect both temporal and cell-type specific transcription. The sporulating bacterium is divided into two compartments (forespore and mothercell) within which different sets of genes are expressed. In addition to the sporulation-specific induction of sigma factor synthesis, the activity of each sigma factor is regulated. Regulation of sigma factor activity is used to synchronize the different programs of gene expression in the two cellular compartments during development. The mechanisms that coordinate sigma factor activities in the forespore and mothercell are not completely understood, but appear to involve targeting of proteins to specific subcellular locations where they provide the conduits for intercellular signaling. We will investigate the mechanisms of promoter activation by Spo0A, a DNA binding protein, to understand how it interacts with two different sigma factors to affect both temporal and cell-type specific activation of promoters. We will also investigate the mechanisms involved in the intercellular signaling between sigmaE in the mothercell and sigmaG in the forespore, especially the mechanisms that target the signaling proteins and others made in the mothercell to the forespore. Elucidation of the mechanisms that control the temporal expression of genes, and synchronize developmental programs of gene expression in Bacillus subtilis may lead to the discovery of novel mechanisms that regulate gene expression not only in endospore-forming pathogens but also in a wide variety of microorganisms.
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