9417735 Haldenwang The occurrence of multiple RNA polymerase specificity determinants (sigma factors) within an organism represents a powerful mechanism for gene control. The substitution of one for another of these proteins on core RNA polymerase can activate or suppress a large number of genes by a single regulatory event. At least ten unique sigma proteins are present in the bacteriumBacillus subtilis with four of them synthesized only during a simple form of differentiation (sporulation) that the bacterium undergoes in response to nutritional stress. The sporulation-specific sigma factors replace the vegetative cell sigmas on RNA polymerase and are the chief activators of sporulation gene expression. In this project the investigator will study the mechanisms by which sigma factor substitution is regulated to properly time the program of spore gene expression. Specifically the experiments will address the processes by which the principal vegetative cell sigma factor (sigmaA) is excluded form RNA polymerase and a predominnant sporulation-specific sigma factor (sigmaE) is activated to replace it. Immunological and biochemical approaches will be undertaken to ask whether sigmaA's activity is masked by modification or sequestration into an inactivating complex. A detailed genetic study using localized mutagenesis and suppressor analysis will be used to discover the developmental signals and factors involved in sigmaE activation. This experimental approach will be supplemented by biochemical and immunological experiments, where appropriate. Spore gene control by sigma factor substitution represents an extremely tractable system in which to study sequential gene expression in a differentiating cell. The devices thatBacillus employs to communicate ongoing morphological development to its transcriptional machinery will likely give insights into how these processes are controlled in a variety of systems. %%% The means by which cell differentiation is controlled continues to be a centra l topic in biology and a focus of much research. In this project the investigator seeks to further our undersandng of this basic process through studying the devices employed by the bacterium Bacillus subtilis to enable it to respond to environmental stress by switching form vegetative growth to sporulation. ***
