Genetic, biochemical and immunological approaches will be used to investigate the genetic and biochemical bases for the virulence of the Streptococcus mutans group S. mutans, S. sobrinus, S. cricetus, and S. rattus of cariogenic bacteria. S. mutans DNA has been and will continue to be cloned into appropriate Escherichia coli K-12 hosts. Clones specifying information thought to be important in contributing to the ability of S. mutans to colonize and display virulence will be characterized. Methods will be developed using cloned gene probes to quantify mRNA levels to investigate regulation of S. mutans genes for colonization and virulence attributes and for enzymes of intermediary carbohydrate metabolism. The specific projects to be pursued are to: (i) continue molecular genetic analysis of the spaA gene and biochemical characterization of the SpaA protein in relation to its functions and interactions with other surface macromolecules, (ii) continue molecular genetic analysis of the dex gene and to characterize dextranase and its endogenous inhibitor to define their roles in adherence and in glucan synthesis, (iii) continue modification of the asd gene encoding beta-aspartate semialdehyde dehydrogenase for use in cloning vectors and to establish mechanism(s) for regulation of the asd gene in relation to pyrimidine synthesis and cell wall assembly, (iv) clone genes for the phosphotransferase system (PTS) and conduct studies to establish mechanisms for sugar transport and utilization, and (v) clone genes for glycogen synthesis and breakdown and conduct studies to determine how these genes are regulated. These studies will contribute to understanding how S. mutans maintains metabolic activity, including ability for acid production, in the plaque environment with variation in the availability of nutrients and in response to activities of other plaque microorganisms. These studies should also provide information on how S. mutans protects itself when exposed to environmental stresses, especially those that interfere with cell wall or cell membrane synthesis or function. The research will be done in conformance with the NIH guidelines for recombinant DNA research.
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