Sex pheromone plasmid pAD1-encoded surface exclusion protein of Enterococcus faecalis

During conjugative transfer of sex pheromone plasmids of Enterococcus faecalis a so-called surface exclusion protein reduces the frequency with which these plasmids are transferred to cells already possessing the same plasmid. We report here the DNA sequence of a 3.8 kb fragment of the sex pheromone plasmid pAD1 containing the structural gene sea1 for surface exclusion protein and a small open reading frame (ORF) upstream of sea1. Surface exclusion protein Sea1 was found to be highly homologous to the surface exclusion protein Sec10 encoded by the sex pheromone plasmid pCF10. Hybridization studies with DNA probes derived from the structural gene sea1 demonstrated that, with the exception of pAM373, all known sex pheromone plasmids carry a homologous gene. These studies also indicated that the genetic organization is similar in these plasmids, with the structural gene for surface exclusion protein being located 5' to that for aggregation substance.