CLONING AND MOLECULAR ANALYSIS OF GENES AFFECTING EXPRESSION OF BINDING SUBSTANCE, THE RECIPIENT-ENCODED RECEPTOR(S) MEDIATING MATING AGGREGATE FORMATION IN ENTEROCOCCUS-FAECALIS

Transfer of the conjugative plasmid pCF10 in Enterococcus faecalis str ains involves production of a plasmid-encoded aggregation substance on the surface of donor cells in response to stimulation by a pheromone secreted by recipient cells. Aggregation substance then facilitates at tachment to recipient cells via a chromosomally encoded receptor, term ed binding substance (BS). A BS mutant, strain INY3000, generated by r andom Tn916 insertions, was previously found to carry copies of the tr ansposon at four unique sites (K. M. Trotter and G. M. Dunny, Plasmid 24:57-67, 1990). In the present study, DNA flanking the Tn916 insertio ns was used to complement the BS mutation of INY3000 following Tn916 e xcision from cloned chromosomal fragments. Complementation results sho wed that three of the four regions mutated in INY3000 play some role i n BS expression. Tn5 mutagenesis and DNA sequence analysis of the comp lementing fragment from one of these regions indicated the presence of three genes (ebsA, ebsB, and ebsC) that affect BS expression. The ebs A and ebsB genes encode peptides likely to function in cell wall metab olism, whereas ebsC may encode a product that suppresses the function or expression of EbsB.