The increasing incidence of antibiotic resistance in bacterial pathogens, coupled with a continuing decrease in the rate of introduction of new antimicrobial agents, constitutes one of the most serious problems in modern Medicine. The research carried out under this grant involves the study of the most efficient system for rapid dissemination of resistance determinants known in the bacterium Enterococcus faecalis, a species which is the most important contributor to the emergence of resistance in gram positive bacterial pathogens. This research is focused on the molecular and genetic basis for the ability of a small peptide pheromone produced by plasmid-free cells to induce donor cells carrying the antibiotic resistance plasmid pCF10 to transfer a copy of the plasmid to a recipient. This form of cell-cell communication is highly complex, specific, and efficient. The research proposed in this application will focus on several of the key components involved in control of the pheromone response, and how they function at the molecular level. The specific aims are as follows: 1. Elucidate the molecular mechanism by which pheromone binding to the pheromone receptor protein PrgX leads to induction of conjugation functions. 2. Determine the mechanism by which the pCF10-encoded Qa regulatory RNA inhibits extension of transcription of the pheromone-inducible conjugative transfer operon. 3. Determine the mechanism of action of PrgY, a novel membrane protein that acts at the cell surface to prevent self-induction in donor cells by endogenously produced, cell-associated pheromone.