This project is a collaboration between the teams of R. Cunin and of M. Crabeel (Genetics and Microbiology (MICR), VUB), of L. De Vuyst (IMDO, VUB) and A. Goldbeter (Unit of Theoretical Chronobiology, ULB). It will analyze the metabolic control of arginine biosynthesis in the bacterium Escherichia coli and in the yeast Saccharomyces cerevisiae, using an approach integrating theoretical system modeling and direct experimental methods (biochemistry, genetics, molecular biology), with iterations of perturbations of the system, monitoring of parameters (product and metabolite pool sizes, enzymatic activities), and further modeling. The different teams have complementary expertises. MICR is specialized in microbial physiology (in particular, regulation of arginine and pyrimidine metabolism), molecular genetics and enzymology. IMDO is specialized in the physiology of industrial microorganisms and the control of fermentation processes, including modeling, and has expertise in the measurement of metabolites. Theoretical Chronobiology is specialized in the theoretical modeling of cellular systems and has applied this approach, which resorts to the rapidly developing field of computational cell biology, to the description of various cellular processes.