Shigella are bacterial pathogens of man which are the causative agents of bacillary dysentery. Over 200 million cases are reported annually and about 650,000 persons die of shigellosis each year. No effective vaccine exists. Shigella is a classic example of an invasive, facultative intracellular pathogen which coordinately regulates expression of its virulence genes in response to environmental signals. The long term objectives of this proposal are to address two areas of pathogenesis: how Shigella regulates expression of its virulence genes in response to environmental stimuli and how certain essential virulence gene products are transported (via a type III secretion system) across the bacterial membrane. The specific aims are to: 1) examine the mechanisms by which Shigella regulates its virulence genes in response to temperature; and 2) elucidate the mechanism by which components of the type III secretion system of Shigella interact and recognize virulence proteins which are targeted for secretion. Several models and experimental strategies for testing them are proposed. Genetic and biochemical approaches for measuring DNA-protein interactions will be utilized in the first aim. For aim two, interactions between components of the type III secretion machinery will be detected by use of the two-hybrid system while mutant selection will be applied to define secretion signals recognized by this pathway. This research will fill in important gaps in our knowledge of Shigella pathogenesis. An understanding of the mechanisms that control expression of temperature-regulated virulence genes in Shigella can lead to the development of specific drugs that block expression of virulence by disrupting the temperature sensing system. Information on how bacteria like Shigella recognize and secrete virulence factors can reveal novel targets for the design of new therapeutic agents against these pathogens.