Many bacteria regulate the expression of genes whose products are responsible for metabolizing nitrogen-containing compounds. In the gram-negative bacteria, many such genes are controlled by a common, intricate regulatory system. Very little is known about how such processes are controlled in gram-positive bacteria. The proposed work seeks to explore possible mechanisms by which the genes for glutamine synthetase and glutamate synthase are regulated in Bacillus subtilis. These enzymes play central roles in nitrogen metabolism and in linking carbon and nitrogen metabolism. The genes for these enzymes have been cloned and have been shown to be under a form of transcriptional control that makes their expression responsive to the availability of certain nitrogen sources. For the glutamine synthetase gene genetic evidence has been obtained that the product of the gene represses its transcription when nitrogen is in excess. This apparent autoregulation will be tested by in vitro transcription to understand the mechanism by which glutamine synthetase acts and to learn the identities of metabolites that might serve as co-repressors. For the glutamate synthase genes, it appears that a neighboring gene might code for a factor necessary for their transcription. This will be examined in detail and other potential regulatory proteins will be searched for. Once the regulatory proteins for the glutamine synthetase and glutamate synthase genes have been identified, their possible involvement in regulation of other genes will be tested. These studies are designed to elucidate a fundamental process in cellular metabolism, to demonstrate novel mechanisms of control of gene expression, and to extend to an important group of bacteria the analysis at the molecular level of regulation of metabolic functions.
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