Further studies will probe the resourcefulness of the Escherichia coli genome to evolve pathways for exploiting novel carbon and energy sources and to discover the range of genetic mechanisms available. The fuc regulon, specifying L-fucose utilization, is under positive control by the fucR product. The enzymes encoded by the fuc structural genes have potentials to catalyze the utilization of fucose analogs, such as D-arabinose and L-galactose. Mutations in fucR can alter the inducer specificity of he activator so that these analogs can be metabolized by the fucose system. The nature of numerous fucR mutations that enlarge the metabolic repertoire of the cell will be characterized. The fucO gene encodes and NAD-linked L-1, 2-propanediol oxidoreductase. The normal function of this enzyme is to produce propanediol as an end product of fermentation. Propanediol, however, cannot be salvaged for aerobic growth because it cannot induced fucO expression. Moreover, the enzyme is inactivated during aerobic metabolism. Mutants serially selected for aerobic growth on propanediol synthesize constitutively and oxidoreductase which is resistant to inactivation. Attempts will be made to characterize the structural changes of the oxidoreductase that render the enzyme resistant to aerobic inactivation. Further studies will be undertaken to depict the agents that inactivate the fucO gene product. Ethanol dehydrogenase, encoded by adhE, is another NAD-linked fermentation enzyme. In contrast to fucO, little is known about the transcriptional control of adhE, except that its expression is 10-fold elevated during anaerobic growth. However, like propanediol oxidoreductase, the enzyme is also inactivated by aerobic metabolism. Mutants that utilize ethanol dehydrogenase for growth on ethanol were first isolated by D. Clark and coworkers. Studies will be undertaken to characterize the mechanism of transcriptional control of adhE and to discover the factors that influence the aerobic stability of adhE gene product.
Showing the most recent 10 out of 13 publications
