DESCRIPTION: The objectives of the studies outlined in this proposal are (1) to determine the mechanisms of plasmid stabilization by the kil loci, (2) to reveal the functions of the twelve gene products expressed by the kil loci, and (3) to understand the host-specificity of these systems. In addition, the incC and korB genes of the korA operon will be studied for their possible involvement in active partition of RK2. For each system, the essential genes and sites will be identified and characterized in detail by genetic analysis. The experiments will determine whether stabilization occurs by active partition, plasmid addiction, multimer resolution, or by novel mechanisms. A variety of genetic approaches (yeast two hybrid assays, suppressor mutants, toxicity-resistant mutants) and biochemical approaches (affinity chromatography, coimmunoprecipitation) will be used to detect interactions among plasmid proteins and between plasmid and host proteins. Each system displays unique properties that will be exploited for analysis.