Abstract
Expression of metabolic enzymes increases the metabolic capabilities of the cell, but it alsoconsumes resources, and the gene regulatory systems of cells have to handle this tradeoff. To studywhether gene expression patterns reflect the varying metabolic needs of the cell, we translatedgene expression profiles into sets of active biochemical reactions, which constitute the expressedmetabolic subnetworks. The metabolic capacity of a carbon source denotes the number of metabolitesthat can be produced from this carbon source and some inorganic nutrients. We studied themetabolic subnetworks that are expressed during diauxic shift in yeast and found that the capacitiesof different carbon sources tend to decrease during the diauxic shift. The subnetwork expressedin the initial glucose environment shows a high capacity of glucose, much higher than networks ofthe same size arising in later stages of the diauxic shift or from a random selection of reactions.The same holds for the essential capacity, the number of important, constitutive compounds thatcan be produced from glucose. These findings indicate that gene regulation increases the rangeof essential compounds that can be obtained from the available nutrients, while minimising the number of expressed enzymes and therefore the burden of protein synthesis.
