The long-term objectives of this research are to analyze the pathways of nitrogen metabolism, their regulation, and their integration with other pathways in the model organism E. coli. The first specific objective is to construct and characterize mutants with defects in the Lrp-regulated ammonia-generating reactions, in order to test the hypothesis that a major function of Lrp is to control the major ammonia-generating reactions in bacteria. Although these reactions necessarily coordinate carbon and nitrogen metabolism, they have not been identified and characterized. The results might establish a new paradigm for bacterial nitrogen assimilation, since Lrp also controls the well-known nitrogen-regulated (Ntr) response. The second objective is to understand the metabolic basis for the stimulation of nitrogen-limited cells by aspartate and citric acid cycle intermediates. The results will further our knowledge of the coordination of carbon and nitrogen metabolism, of the factors that limit bacterial growth, and of the metabolic potential of E. coli and other bacteria. The third objective is to use commercially available genomic arrays to analyze the pattern of gene expression during nitrogen limitation. The results will test and refine our understanding of the coordination of nitrogen metabolism with other aspects of metabolism (such as carbon metabolism) and the function of Lrp. The results might also help identify Nac-regulated genes and thereby help formulate a physiological function for Nac, which activates several genes during nitrogen limitation.
All cells require highly complex regulatory networks to coordinate the vast number of metabolic activities that constitute their lives. This project will deepen our understanding of one of the most important of these networks, that coordinating carbon and nitrogen metabolism. Knowledge of these networks is an important part of the foundation of virtually all our scientific endeavors.
