The Enterococcus faecalis plasmid pAD1 conjugatively transfers in response to a sex pheromone, cAD1, excreted by potential recipient cells. A key determinant responsible for regulation of pAD1 transfer is traA, which encodes a negative regulator also believed to function in signal sensing. In this study, we analyzed the nucleotide sequence and transcription of traA. A protein of 319 amino acids with a molecular weight of 37,856 was inferred and found to exhibit limited homology with several DNA-binding proteins. Analysis of Tn917-lac insertions resulting in transcriptional lacZ fusions within the 3' end of the traA transcript showed that it overlaps slightly with a convergently-transcribed C-region transcript. Insertional mutations affecting TraA repressor function and signal sensing functions were localized.