Conjugative transfer of Enterococcus faecalis plasmid pAD1: nucleotide sequence and transcriptional fusion analysis of a region involved in positive regulation

Abstract

The Enterococcus faecalis plasmid pAD1 undergoes conjugative transfer in response to cAD1, a peptide sex pheromone emitted by potential bacterial recipients. Regulation of pAD1 transfer involves a number of plasmid-encoded determinants:iad, which determines a peptide-competitive inhibitor iAD1; signal sensing and transducing elements; and negative and positive regulators. The key positive regulator(s) of the pheromone response is believed to be encoded within a segment designated the E region of the plasmid. In this study, we analyzed the nucleotide sequence and transcription within the E region. An open reading frame designated traE1 was identified; its inferred protein consists of 118 amino acids. Insertional mutagenesis of traE1 resulted in a complete loss in plasmid transfer capability. Analysis of Tn917-lac insertions giving rise to transcriptional lacZ fusions showed that traE1 is transcribed only under cAD1 inducing conditions. Analysis of additional lacZ fusions within the region provided some insight into the roles of potential regulatory signals within and around the nucleotide sequences reported here. A regulatory role appearing to involve read-through of certain key transcription termination sequences seemed evident.