We have two major research interests. (1) DNA-protein interactions in Mu transposition. Many cancer-causing retroviruses including HIV recombine with their host genomes in a manner similar to that used by transposable phage Mu. Assembly of a functional Mu transposase tetramer requires binding of the protein to Mu ends and also to a distantly located enhancer element. Several nucleoprotein complexes called transpososomes have been identified along the transposition pathway. Our current research goal is to understand the architechture of these transpososomes, why the enhancer remains associated with them until the completion of transposition, how target DNA is delivered to this complex, and what the similarities and differences are between the Mu and HIV integration systems. A combination of molecular genetics, biochemistry, and structural studies is being pursued. (2) Swarmer- cell differentiation in Salmonella typhimurium: a model for understanding surface signal transduction and pathogenesis. When this bacterium is propagated on a solid agar surface it differentiates into a specialized swarmer cell which is longer and has more flagella than a vegetative cell. Swarmer cells display a group surface motility that enables them to rapidly colonize the agar surface. The swarming colony lives within a biofilm. We have discovered that under these conditions, the well-known chemotaxis system is not required for chemotaxis, but rather for surface signal transduction. Microarray analysis is revealing interesting parallels between the biogenesis of flagella and that of needle-structures during swarming. Needle structures are distinct organelles that resemble flagella, but are specialized delivery vehicles for virulence proteins during infection of a host. Our experiments are aimed at understanding the molecular mechanism of this new pathway of signal transduction, investigating the similarities and differences between moving and adherent biofilms, as well using swarming as a model system for the analysis of virulence protein secretion.