The highly conjugative pAD1 plasmid encodes a mating response to the peptide sex pheromone cAD1 secreted by recipient strains of Enterococcus faecalis. The location of the origin of transfer (oriT) was determined through the ability to mobilize the Escherichia coli-E. faecalis shuttle plasmid pAM401 carrying specific segments of pAD1. The oriT sequence was found to be completely within the repA determinant known to be required for plasmid maintenance. (C) 1997 Academic Press.