THE PRGQ GENE OF THE ENTEROCOCCUS-FAECALIS TETRACYCLINE RESISTANCE PLASMID PCF10 ENCODES A PEPTIDE INHIBITOR, ICF10

Conjugative transfer of the Enterococcus faecalis tetracycline resista nce plasmid pCF10 is stimulated by a peptide pheromone, cCF10. Once a recipient strain acquires pCF10 and thus becomes a pheromone-responsiv e donor, cCF10 activity is no longer detected in culture filtrates. He re we show that pCF10 encodes a peptide inhibitor, iCF10, secreted by donor cells; this inhibitor antagonizes the cCF10 activity in culture filtrates. In order to detect and quantitate iCF10, we developed a rev erse-phase high-performance liquid chromatography assay in which the i nhibitor peptide elutes separately from the pheromone; this type of as say enabled us to determine that lack of pheromone activity in donor c ulture filtrates was due to secretion of a mixture of iCF10 and cCF10, rather than abolition of cCF10 secretion. The gene encoding iCF10, pr gQ, is located on the EcoRI-C fragment of pCF10. The open reading fram e comprising the prgQ gene encodes a 23-amino-acid precursor that rese mbles a signal peptide. This precursor is cleaved to the mature heptap eptide iCF10 during the secretion process.