Bacteria have a complex information processing system that allows them to respond to changes in specific chemicals in their environment by modifying the pattern of flagella rotation and thus regulating their motility. Many of the genes that encode specific proteins in this pathway have been identified, sequenced, and their gene products overproduced. A family of transmembrane proteins plays a central role in this process. They interact with specific ligands and transduce these interactions into signals that affect flagellar rotation. They are analogous in structure and function to cell surface receptors found in a variety of other prokaryotes as well as in complex eukaryotic systems. We plan to continue to focus our attention on this family of signal transducing molecules in order to determine how they function. We will use a variety of techniques to specifically mutagenize these genes and study the effects of mutated gene products on the function of the transducers and their interaction with other components of the chemotaxis pathway. We will develop techniques for studying the function of these proteins in vitro and methods for measuring the coupling between ligand binding events, signalling and the reversible methylation of the transducer. We hope to understand how these molecules transmit information across the cell membrane and transduce this information into a change in the chemistry of the cells.